Before he was denounced as a thief and cast out of the hedge fund industry, before he was a Goldman Sachs banker or a maths prodigy, Ke Xu was a little boy in Hubei province, who loved puzzles. His parents, junior government clerks, didn’t have much money, so Xu would scour the house to find old algebra and science textbooks. He spent hours with the series 100,000 Whys, children’s brainteasers with a Maoist flavour. The commune wants to build 40 tractors – how many wheels should it buy?
When Xu was 16, his head teacher identified him as a gifted student and recommended him for a scholarship at the Raffles Institution, in Singapore, a prestigious British-style boarding school with the Latin motto Auspicium melioris aevi (“Hope of a better age”). Xu mastered English and cruised through his classes, if not the school’s extracurricular activities. Cricket was a mystery he could never solve.
After Raffles he moved to Britain to study mathematics at Cambridge University, eventually graduating third in a class of 250. Then, thousands of miles from home and with no enticing career ideas of his own, Xu took the advice of a professor who had worked in the City of London’s financial district and applied to Goldman Sachs’ programme for graduates.
He joined the investment bank on the eve of the 2008 financial crisis and soon impressed his colleagues with his quick thinking and work ethic. The others on the credit derivatives pricing team were much like him, maths geeks from modest international backgrounds. Although Xu enjoyed the work, he didn’t find it challenging, and he didn’t fully embrace the Goldman Sachs gospel of money and power. On LinkedIn, he listed his job title as “dude” and one of his skills as “bread and butter making”.
Standing a little over five feet tall and wearing glasses, Xu was unimposing, but his confidence was ironclad. “I am born as a superstar stats trader [...] mathematical, commercial, hardworking, competitive, visionary and mentally tough,” he once boasted to his girlfriend, Mengyang, according to evidence from a lawsuit against him. “I have to live up to the great expectations that I have set for myself.”
By 2012, credit derivatives were out of fashion, and he decided it was time for something new. Then 28, Xu applied for jobs around the City and was offered a position by G-Research, part of a web of companies formerly known as the De Putron Fund Management Group, after its founder, Peter de Putron, a reclusive British hedge fund executive. G-Research’s website casts the company as a leader in quantitative research, with the slogan “Create today. Predict tomorrow”.
The underlying fund was as mysterious as its founder. Xu and his new colleagues knew little about its workings or how much it was worth. But they knew, from the tight security in the office and the imposing non-disclosure agreements they were asked to sign, that their work was extremely valuable.
Quantitative trading is distinguished more by process than style. A quant strategy is the product of rigorous scientific research, using computing power to identify price mismatches and to run simulation after simulation in search of trades promising the biggest pay-off with the least risk. The intention is to automate out the human flaws – greed, fear, indiscipline – that make markets fail. But computers can do only what they’re programmed to do, so human endeavour remains vital.
Xu found the work isolating. He spent his days writing code in the G-Research “secure zone”, which could be entered only through a special pod with a biometric finger scanner and a weight sensor designed to detect unauthorised equipment entering or leaving the area. He understood the hedge fund had few external backers and so functioned essentially as his boss’ private investment office.
De Putron, known to his employees as P de P, called in daily to check how much money he’d made or lost. Fair-haired, with a runner’s frame, he occasionally appeared in the office dressed casually in a white shirt, jeans and trainers. To Xu he seemed genial and aristocratic, with manners polished at Eton College, Britain’s most prestigious private school.
Xu’s first bonus, awarded a few months after joining G-Research, shattered any illusions that he’d reached the hedge fund elite. “Bonus only 3k,” he said in an online message to Mengyang. “F*** me, why? Only December, but it is still crap, crap, crap, crap. It should be more.”
He set his formidable intellect to the task, working weekends and updating his supervisor, Ben Handley, so often he was admonished for the constant interruptions. He came up with 20 trading strategies – “signals” in quantspeak – and tested each in endless simulations. Seven proved profitable enough to be adopted by the parent fund and put to work.
At the start of 2014, as his second-year bonus announcement neared, Xu was feeling optimistic. “If I get 1.1 million this year, next year should be 3.3 million,” he told Mengyang. “Next year it will be 16 million, then 100 million.” Instead, Handley told him he’d been awarded £400,000 (HK$4 million), a huge sum for a young man from provincial China but far less than he was expecting.
Xu’s dedication had been testing a romantic relationship further strained by his distance from Mengyang, who was working as a corporate lawyer in Hong Kong. “I really love you, but I also have to win,” he wrote to her at one point. After getting word of his bonus, he decided that, instead of spending hours on the phone with her each week, he would quit and return to China. He’d be closer to her, and Asia seemed a better fit for his ambition.
It was around this time, while he was planning his exit, that Xu began covertly accessing his colleagues’ signals. Exactly why he did so is disputed. G-Research would later accuse him of stealing trading strategies so that he could use them for himself or at a rival company; Xu would testify that he was suffering from coder’s block and needed inspiration. But he also acknowledged that he had a better chance of getting a good job elsewhere if he had ready-to-use signals to offer potential employers.
There was a problem, though, beyond the physical security protocols at the G-Research office: the company scrambled the code that ran its trades, specifically to prevent it from being copied. So Xu built a decompiler that could translate it. For months in 2014, while still in G-Research’s employ, he put on sweatpants and worked remotely, logging in to its system from his flat in an unglamorous district of south London.
He spent 336 hours – 14 full days – logged on in March. In April and again in May, it was 15 days; in June, 17. On one screen, he’d watch his employer’s secrets unfold. On another he’d play videos by his favourite band, Phoenix Legend, a Chinese folk-pop act pairing a traditional female singer with a shaven-headed rapper. At the same time, he was looking for a new job. He landed two offers in Asia but told his managers at G-Research nothing of his plans.
A bright future seemingly assured, Xu and Mengyang married at London’s Ritz Hotel that July, with their parents in attendance. On July 29, Xu’s mother flew back to Hubei with her luggage bulging. Inside were several electronic devices her son had given her, including a desktop PC.
One evening the following week, Xu cleared out his desk at G-Research, loading documents and a notebook into a suitcase. Then he placed a resignation letter on Handley’s desk. “Dear Ben,” the letter read. “It has been a pleasure and a real joy to work at G-Research.” Xu praised the company’s competitive pay and said he was leaving for family reasons with “no immediate plans for other things”. He stopped at his flat to log on to the system one last time, then boarded a flight to Hong Kong.
The abruptness of Xu’s departure raised immediate suspicions. The next morning security personnel at G-Research reviewed video footage of his activities the night before, leading the company’s lawyers to obtain an emergency court order requiring Xu to return anything he had taken and turn in his passport. By then, he was already cruising at 30,000 feet.
De Putron’s company swiftly put Allen & Overy LLP, a top-flight law firm with offices around the world and a reputation for aggressively defending its corporate clients, on the case. When Xu landed at Hong Kong International Airport, Allen & Overy had someone waiting to confront him. “Are you Mr Xu?” the man asked. Xu said he wasn’t and hurried to the taxi queue.
The lawyers went to a Hong Kong judge and had a travel ban imposed on Xu. The hedge fund was concerned that he had downloaded the software running its algorithmic trades, to either use himself or hand to a competitor. The market opportunities identified by quants always close; how quickly depends on the number of traders exploiting them. Anyone using De Putron’s strategies would in effect be taking money out of his pocket.
The following day, Xu returned to the airport to fly to the mainland. He was told that he would not be allowed to leave. Instead he made his way to a railway station near the border, where he met his wife’s mother and father. He gave them a desktop computer and three laptops. “Give them to my parents,” he said. Before departing, they handed him a rack of lamb encased in a foam box – a small taste of home.
It didn’t take long for Allen & Overy to track down Xu, this time in the lobby of his wife’s law firm, Linklaters. A representative told him he was required to reveal the location of his suitcase, documents, and any electronic devices in his possession. Xu replied that his only device was an iPhone.
G-Research’s next move was to report him to the police in London, who searched his apartment and made contact with officials in China. On August 14, Hong Kong police appeared at Xu’s wife’s flat to arrest him. He was expecting them. One of the officers found the box of lamb and asked if there were body parts inside. Obviously not, Xu replied. They took him to jail.
When British police requested Xu’s extradition to the UK to face criminal charges, he agreed to return willingly. Whatever is going to happen, he thought, I want it to be over as soon as possible. In December 2014 he returned to Britain flanked by three policemen in the back row of a commercial flight.
Back in London, Xu was denied bail. He remained in custody until the following June, when he pleaded guilty to fraud. In his statement, he admitted to reverse-engineering 55 G-Research trading strategies for personal gain. On July 3 he was sentenced to four years in prison. With parole and time served, he could expect to be released in a year. “Most of the people who appear in front of me could only dream of the sort of bonuses from which you would have continued to benefit for many years to come,” the judge said.
Throughout the case, Xu had denied keeping G-Research’s code, showing it to anyone, or making copies, beyond some handwritten notes police found at his flat. The problem was, his former bosses didn’t believe him.
On any given day, algorithms are responsible for about 95 per cent of transactions on American stock exchanges. The shift away from humans to machines has presented a profit opportunity for the most sophisticated banks and hedge funds, but also a headache. With strategies worth billions of dollars now capable of slipping out the door in a pocket-sized device, finance companies and legal systems alike have struggled to respond.
The few high-profile cases of code theft there have been have been handled inconsistently, with judges and prosecutors disagreeing over what constitutes digital crime. Sergey Aleynikov, a Goldman Sachs programmer accused of downloading thousands of lines of code, was convicted, acquitted and convicted again during a six-year legal roller-coaster ride through the New York court system. He served one year of an eight-year prison term before being released in 2012. In another case, a Chinese quant accused of stealing from Two Sigma Investments LP in New York received 10 months; with his time already served, he flew home soon after being sentenced.
In Britain, aggrieved financial companies have another tool to deploy in defence of their secrets: an ancient quirk of the legal system called a private prosecution. This approach allows the purported victim of a crime to investigate and prosecute the perpetrator if the state fails to do so.
In theory, private prosecutions are available to anyone who wants to bring a criminal complaint. They have been launched in the past by the parents of a murdered teenager and a conservative activist who accused a gay media outlet of blasphemy. But building a case is expensive, so the practice is now used mostly by businesses and others with a few million pounds to spare.
The Ministry of Justice does not keep precise statistics on private prosecutions; senior British judges have said they have noticed an increase recently, as state agencies struggle to deal with more complex frauds and a lack of funding. Critics have warned that any such rise risks creating a two-tiered justice system that better serves the rich. However, there are safeguards. The attorney general, state prosecutors and judges can all stop a case if it is spurious or not in the public interest.
De Putron’s companies saw their chance to intervene in the Xu case when, during sentencing, the judge issued an order under proceeds-of-crime laws, forcing Xu to give up any confidential information he still held and reveal whom he had shown it to. If he did not comply, he would face more time in jail. Seeking to enforce the judge’s order, London police detectives hauled Xu out of prison for an interview in December 2015. He answered all their questions with “no comment”.
With the police investigation seemingly stalled, G-Research began a private prosecution to find out who had seen the 55 stolen signals and what was stored on the computers sent to China. The company hired private investigators, specialist lawyers and forensic IT experts, gathering enough evidence to bring the case to court. In July, a year after Xu had been sentenced and a month before he might have expected to be released, he was summoned from HM Prison Wandsworth, charged with breaching the criminal-proceeds order, and returned to his cell.
The trial began in December. Xu stood accused of five counts pertaining to the missing computers and code and to his failure to reveal who knew about the signals and where he was keeping any copies. Although a hedge fund was paying G-Research’s lawyers’ bills, they spoke to the jury, per the norms of private prosecutions, as representatives of the Crown – the British government.
Xu, appearing as a witness for the first time, denied having copies of G-Research software. Asked whether he had shown anyone the signals, which the company conservatively estimated were still worth about £30 million, he replied, “No. It would mean trouble for them. It would mean trouble for me.” He then offered a series of bizarre explanations for why he could not return the devices he had sent to China. One had been loaned to a relative and subsequently stolen, he said. His parents had thrown others in the Yangtze River. When he explained that one computer had been cremated alongside a deceased uncle, the courtroom erupted in laughter.
G-Research’s lawyers also questioned Xu about the job offers he had received before leaving Britain. One had been from Cubist Systematic Strategies, a unit of Point72, a private hedge fund run by billionaire Steven Cohen. Cohen was emerging from his own brush with scandal, as Xu knew well. Although Cohen himself was never charged with anything, several employees at his previous company, SAC Capital Advisors, had been convicted during an insider-trading probe, and it had pleaded guilty and paid a US$1.8 billion fine to resolve the charges.
In June 2014, Xu testified, he had flown to Connecticut, in the United States, for an interview and met Cohen briefly in his office, surrounded by trading screens. Cohen told Xu that Point72 was a meritocratic place and that if he worked hard he would be rewarded. “Everybody loves me, especially Steve,” Xu told his wife.
He rejected G-Research’s insinuations that he had offered Cubist any confidential strategies because, he said, he believed Cohen would not risk using them. “He already paid a huge price before,” Xu told jurors. “He would never make the same mistake again.” Point72 declined to comment for this article.
When Xu’s elderly mother, Lu Juanhe, testified by videoconference from a law office somewhere in China, the internet connection repeatedly failed. When it was finally established, it took several minutes to swear her in, an English lawyer asking the courtroom translator to ask a Chinese lawyer to ask Lu if she promised to tell the whole truth.
The questioning continued in this vein, with Lu explaining that the computers she had received from her son – five in all, plus a hard drive, an iPhone, and some memory cards – were gifts that she considered her property. She recalled that a lawyer had visited her home in an attempt to retrieve them, making her so angry that she woke at 5am on December 30, drove to the Yangtze with her husband, and hurled several of them into the water.
G-Research lawyer James Hines challenged Lu. “You didn’t leave the house at all that morning, did you?” he said.
She asked how he could know that.
“You were being watched by private detectives,” he replied. Lu appeared stunned.
“How did you send this private detective?” she asked.
“They were watching you,” Hines said.
It emerged that Chinese detectives had tracked Lu and her husband for 11 months. Two of the investigators testified that they had rented a nearby flat and watched the couple in shifts from a car. They had taken photos such as one they showed of Xu’s father, a retired accountant with heart trouble, captioned, “Target playing Mahjong from 1.00 to 5.00”. The investigators also produced photos they had shot of the couple’s front door every hour starting at 4.28am on December 30, to establish that they had been watching that morning.
In January 2017, jurors found Xu guilty of two of the five charges in the private prosecution, deciding that while he couldn’t be held responsible for not returning the computers, he had not properly explained where the stolen information had gone and who’d had access to it. The judge sentenced him to an additional 18 months, saying, “We all know the stakes for which you were playing.”
Had Xu been employed by anyone but De Putron, his legal problems might have ended there. But his former employer was not finished with him yet.
De Putron has never given a media interview, and he declined to do so for this piece. He is a “very private individual”, said his spokesman, Paddy Harverson, in an email. From what little can be pieced together about De Putron from public sources and interviews with current and former employees, he grew up in Guernsey, one of the low-tax Channel Islands wedged between England and France. His father was a local politician, and the family name is part of the island’s lore. A road near the capital, Saint Peter Port, is called Rue de Putron.
Peter de Putron started his hedge fund in 1997, securing seed money from investor George Soros. He got into algorithmic trading “as quickly as he could afford to”, according to Alex Ribaroff, a friend and the former chairman of one of De Putron’s early funds, Centenier (the name given to volunteer police officers in parts of the Channel Islands). “It was an arms race” to develop systems and hire experts, said Ribaroff, who left the fund in about 2000.
The newsletter MARHedge reported in 1999 that the fund was managing about US$100 million; Xu estimated from the witness box that, by 2014, the pool stood at US$3 billion to US$5 billion. A spokeswoman for De Putron disputed this estimate but declined to elaborate. However large the fund, former employees say the money is mostly De Putron’s, though organisations that track the wealth of billionaires, including Bloomberg News, have never included him in their lists.
Even the hedge fund’s name is shrouded in mystery. The spokeswoman said there used to be an entity called De Putron Fund Management, but that it no longer existed and there was no collective name for the group of companies making up De Putron’s business.
The quants working for G-Research in London create algorithmic trading software that is deployed from an office in Guernsey. Traders on the island work in shifts to keep the operation running around the clock, according to one former employee. Their job is to watch software work its magic, checking for errors and making adjustments to account for unexpected market moves. The source said the group made profits of about US$700 million in 2017, a figure De Putron’s spokeswoman also denied, adding, “This information is not in the public domain.”
The few media reports about De Putron focus on his impressive political connections and earlier legal wranglings. His companies have donated more than £600,000 to Britain’s ruling Conservative Party, some of which went to lawmaker Andrea Leadsom, who bid unsuccessfully to head the party in 2016 and is now leader of the House of Commons. Leadsom is married to a De Putron employee, and she worked for De Putron before becoming a member of Parliament, the British press has reported. A spokeswoman for Leadsom declined to comment for this article.
As for the litigation, De Putron filed a defamation suit in 2017 against the owner of The Sun newspaper, accusing it of wrongly linking him to an offshore tax scandal; the paper ultimately published a correction and apologised. He also sued his brother and his brother’s ex-wife over a family loan after their father’s death in 2009 – an action his brother described in an email as in accordance with Peter’s fiduciary duty as administrator of the estate.
At around that time, De Putron became involved in another legal dispute that foreshadowed his companies’ campaign against Xu. The year before, a group of five programmers and managers had left G-Research, then known as GR Software & Research, to start their own trading outfit. The company responded by first threatening a lawsuit, then, in 2011, by filing one. None of the filings suggested theft but G-Research argued that the five had developed their quant-trading skills at the company, and so any new platform would be similar and an infringement of its intellectual property.
The court documents from the resulting litigation opened a rare window into De Putron’s trading empire. In their legal filings, the former employees described De Putron as a “man of vast wealth” and a “secretive person who is paranoid about confidentiality”. From the moment the employees resigned, they claimed, lawyers from Allen & Overy “began a campaign of interminable correspondence and threats of legal action” against them, prompting them to file a countersuit for harassment.
Graham Edwards, an executive who they cast as De Putron’s “right-hand man,” sent them a threatening email, according to evidence from the countersuit. “We will use every weapon at our disposal to stop you selling what we believe is effectively our system to the street,” Edwards wrote. “Win or lose we will certainly delay you, perhaps considerably, and we will also send a strong signal to others not to mess with our IP.”
In 2009, two of the five former employees said in filings that they had found tracking devices on their cars, prompting them to call the police. One also reported being trailed by a blue van as he walked with his wife and son, while others recalled being filmed by men holding mobile phones as they went to the pub. The legal dispute continued until at least 2014, when it was settled on confidential terms. A spokesman for the five employees’ new company, Quadrature Capital, declined to comment for this article.
Xu was aware of the case when he left his resignation letter on Handley’s desk. During his trial, he had told the court he’d heard De Putron was “very, very angry” one of the senior members of the group quit. It was one reason Xu had decided to leave with such haste – he was afraid of what would happen next.
Despite his additional 18-month sentence, Xu could still look forward under Britain’s parole system to getting out a few months after the private-prosecution conviction was handed down. He would then surely be sent back to China, standard practice for foreign offenders. He allowed himself to start thinking about a new life, perhaps working in artificial intelligence. But soon after his sentencing, Allen & Overy wrote to the prison service, opposing probation and calling his behaviour “manipulative, deceitful, self-serving, and an insult to the authority of the court”. At the same time, the company petitioned the Immigration Department to delay his deportation.
When they didn’t get the response they wanted, De Putron’s companies sued the government and began serving prison governors, probation officers and the Ministry of Justice with what the government’s lawyers later complained was an “extraordinary volume of paper” requesting all manner of information about Xu’s case. “Officials deserve ‘protection’ from such resource-sapping and distracting behaviour,” the lawyers wrote in court documents. (A spokeswoman for Allen & Overy said the company actions were proportionate and in keeping with the seriousness of Xu’s offence.)
After Xu’s prison sentence ended, he was sent to an immigration detention centre pending deportation, surrounded by high walls and barbed wire – a prison in all but name. While he sat there, G-Research opened yet another legal front against him, filing a lawsuit in London’s commercial court system that sought restitution for breaching the confidentiality clauses of his contract.
At a pretrial hearing in January 2018, a lawyer for the company told the judge, “What we are trying to do is get to the truth of what really happened.” If a competitor got hold of the strategies, he said, it would cost the hedge fund tens of millions of pounds. He asked that Xu be prevented from leaving the country while the case proceeded.
Appearing without a lawyer and clutching a plastic bag full of documents, Xu cut a pitiful figure. “The defendant has already been punished once,” he told the judge, undercounting by one. “It is excessive to punish him again.” He disputed whether the trading strategies were really as valuable, years later, as the hedge fund claimed.
While the courts processed the cases against him, Xu was granted bail. He walked out of Harmondsworth Detention Centre on March 16, 2018, three years and seven months after he was first incarcerated. His first act as a free man was to order a family bucket from Kentucky Fried Chicken. The same day, Allen & Overy wrote to British immigration authorities asking them to take “all necessary steps” to keep Xu in the country.
Later that month, we met Xu at the modest east London flat where he was staying with a friend. It was a less moneyed part of town, but the skyscrapers of Canary Wharf were visible through the drizzle. He answered the door in a grey tracksuit and sandals. There was a child’s blanket on the sofa, his bed for the moment. He suggested going out for coffee. “I’m not sure if this place is bugged,” he said.
It was easy to see why friends had stuck by him – some of his former Goldman Sachs colleagues even helped fund the early stages of his legal defence. His quirky sense of humour had survived Wandsworth, Britain’s largest prison and one of its toughest. He had seen violence and drug use there, he said, but he was never physically threatened. Boredom and homesickness were his biggest problems. Asked if he’d heard from his wife, Xu said yes, she had served him with divorce papers. He shrugged despondently.
He had been hoping to return to China by the end of 2018, but it hadn’t panned out. “It is difficult to imagine what kind of tactics their lawyers will come up with,” he said. When he finally got home, he added, he wanted nothing more to do with hedge funds.
It was also easy to see why he infuriated his opponents. He could be defiant to the point of arrogance. Asked whether he’d done anything wrong, he replied, “By their rules, I should not have known that much. I knew too much. That’s the thing I’ve done wrong.”
Ribaroff, De Putron’s friend and former chairman, recalled that Peter was “really upset” by what Xu had done. For Ribaroff, who said he was not personally involved in the case, the dispute was about nothing less than London’s future as a financial hub. If companies couldn’t protect complex trading systems, he asked, why invest money in creating them? “You are talking about a lot of jobs that depend on being able to develop something and use it without having it disappear overnight.”
Harverson, De Putron’s spokesman, sent a statement from Trenchant, which is part of G-Research. “Like any other victim of theft, Trenchant has simply followed the legal process to ensure justice is done and that the perpetrator does not profit from his crime. In finding in favour of Trenchant at every juncture, the courts have demonstrated the UK’s ability to defend intellectual property – which is critical to doing business successfully in any country.”
Even G-Research has conceded in court filings that the stolen trading strategies had a shelf life. About half had expired by the end of 2017, and initially the company had asked only that Xu not be set free before August 2018. As that deadline approached, however, the company’s paper war continued. Its lawyers won orders in commercial court requiring Xu to return his salary and bonuses and to reveal what became of the information. When Xu once again denied that there was anything more to reveal, they asked a judge to send him back to prison for contempt of court.
At a hearing in June, Anthony Peto, counsel for G-Research, said Xu was as competitive as Tiger Woods. “He wants to beat not just us but the courts as well,” Peto told the judge. Xu’s lawyer, Stephen Cragg, argued his client had nothing left to reveal. “He can’t work. He can’t study. He can’t go home. He can’t see his wife.” There came a time, Cragg said, “when enough is enough”.
Looking down from the bench later that month, the judge disagreed, declaring that he had no alternative but to impose another prison term, this time of 13 months. “Mr Xu has neither admitted his contempt nor expressed remorse,” he said, noting that Xu could reduce his sentence to one month simply by obeying the court’s orders.
Xu, wearing a striped shirt tucked into sweatpants, frowned in concentration as his fate was decided. While the judge spoke, two court employees quietly entered the room. One, a stout man holding a pair of handcuffs, was the tipstaff, a plain-clothes officer of the court. Xu held out his wrists to be cuffed, then was led away into the maze of corridors that weave through the Royal Courts of Justice. Another official walked behind them, towing a suitcase full of the prisoner’s personal effects.
With good behaviour, Xu should have been eligible for release in December. At the time of going to press, he remains behind bars, and is expected to be released in a matter of weeks. When that time does come, there will be nothing to stop G-Research from asking the court to keep him behind bars.