At his home in Massachusetts, the author read media reports of the lurid details emerging in the murder trial in Hong Kong of a wealthy expat wife named Nancy Kissel. The 41-year-old Michigan-born woman had allegedly drugged her millionaire investment banker husband, Robert Kissel, with a sedative-laced milkshake before bludgeoning him to death with a lead ornament in their luxury Parkview flat on November 2, 2003. Then she rolled his body up in a red carpet and hired four workmen to carry it to a storeroom.

Her motive, the prosecution argued, was to run away with her lover - Michael Del Priore, a TV repairman who lived in a trailer park in New Hampshire - with her husband's estate, estimated to be worth US$18 million.

At that time, the Kissel name was in the US news for another reason. Andrew Kissel, the elder brother of Robert and a wealthy property developer in Connecticut, was arrested for having swindled banks, companies and others out of tens of millions of dollars.

McGinniss, who became a publishing sensation aged 26 with his debut, The Selling of the President - an account of the marketing campaign behind Richard Nixon's presidential election in 1968 - found the Kissel tale too peculiar to ignore.

McGinniss picked up the phone to call Frank Shea, a private detective in New York who was hired by Robert to trace his wife and her lover shortly before his death. That was the start of a two-year research project for Never Enough, an account of the Kissel tragedy that will be published next Thursday.

'I will tell you, having finished this, I have no desire ever to do it again,' he told the South China Morning Post this week in his first interview given on the book. 'The depressing part is sitting in a room with someone, and that person is crying because he or she is suffering a pain that you will never know.'

The journalist-turned-author interviewed Bill Kissel, father of Robert and Andrew. He also spoke to Ira Keeshin and Jean McGothlin, the divorced parents of Nancy Kissel. He also interviewed many friends and relatives of the two grief-stricken families in his quest to gain clues to how the relationship between a happy, wealthy couple could end in murder.

The author found that events became more dramatic as the three-month trial went on. On September 1, 2005, the seven-member jury deliberating on the case returned a unanimous verdict of murder, meaning an automatic life sentence for Kissel. Barely half a year later, Andrew Kissel was found stabbed to death in the basement of his home with his hands and feet bound. Police investigations have yielded few clues about the mysterious killing.

In September last year, McGinniss flew to Hong Kong for a week to talk to the friends the couple had made since they arrived in the city in 1997. Robert was then a rising star at Goldman Sachs before he was poached by Merrill Lynch. Above all, the author wanted to see Kissel, who is jailed at Tai Lam Prison with 12 other lifers. But Kissel rejected his request for an interview and for a copy of the court transcripts. Her defence team cited her appeal, scheduled for April next year, as a key reason for the rejection.

However, McGinniss was given an insight into her thinking when Mr Del Priore agreed to share with him the hundreds of letters she had sent him since she was arrested. The subject matter of the letters - some of which feature in his book - was never far from her longing to reunite with her lover.

'It's like a 13-year-old girl who had a crush on a guy. They were so one-dimensional. She's living in a fantasy world. It made me question her intelligence,' McGinniss said. Kissel rarely mentioned her children and had refused to receive letters from them.

In late 2005, McGinniss drove up to the TV repairman's trailer to introduce himself. During the trial, Mr Del Priore was accused by the prosecution of seeing Kissel as a gold mine. Telephone records showed they rang each other long-distance hundreds of times shortly before and after the murder.

About six months after meeting Mr Del Priore, McGinniss received a surprise call from him one night. The author said Mr Del Priore told him: 'I think I would like to talk to you because everyone who wanted to talk to me has been so rude. They came up here and they don't treat me like a person.'

McGinniss said: 'He denies completely that he ever knew anything. He said Nancy never told him anything about planning to kill Robert and she never told him anything after [what] she had done. He described how she was getting increasingly disturbed, calling him from payphones in Hong Kong, moving from place to place, sure that she was being followed.'

McGinniss believed Mr Del Priore's motivation for giving him access to all Kissel's letters was to clear his name. 'He never said this, but it was as if he was implying to me, 'Here, here, all of the letters. You find one letter where she wrote to me about me knowing anything [about the murder].' I think he felt that reading letters would show that he had been deceived, the same way [Nancy's] family and friends had been deceived by her,' he said.

'I can't say I like Del Priore. But I have not found a monster there. I found a not terribly bright, not terribly appealing human being.'

McGinniss said a major point he made in his book was that the story Kissel told at the trial was very different from anything she had ever said to anyone before. 'I think by just pointing that out, goes a long, long way towards showing people that what she said about Robert in the trial should not simply be accepted as fact,' he said.

The author also said greed appeared to be a key theme. 'The only thing that I ever heard that either Robert or Andrew cared about was making money. They had no interest in politics, social issues, were not involved in charities,' he said. 'They were both totally obsessed with the one goal of making as much money as they could. The big, big, big difference is that Robert did it legally and Andrew did it illegally.'

The author said Robert once told Nancy's father on a trip to Phuket: 'There's no such thing as enough.'

McGinniss said: 'Nancy never left Rob. If he abused her, do you think for one minute she would stay in the relationship? Why did she stay in that relationship? Because of the lifestyle she's married to. It's somebody who got caught up in this whole lifestyle of wealthy expats in Parkview,' he said.

But the author is now facing a barrage of criticism and anger from the key characters in his book. Through her defence team, Kissel said she considered the book to be a distortion of events and a gross mis-characterisation of her and others portrayed in it.

Bill Kissel, 79, who was portrayed by McGinniss as a difficult and unforgiving father who was instrumental in driving his sons to where they ended up, said it was unbelievable that the father suffering from this double tragedy was presented as the 'family villain'. He also accused the author of presenting inaccuracies, and of going beyond poetic licence to ascribe words and thoughts to Robert and himself that had never existed.

The author maintained that he had given an accurate and fair picture of the events from what he had gathered from his interviews. There were many instances where the characters in the book pointed fingers at each other, he said. 'But my larger point is that the Kissel family is a family in which hatred has replaced love. And that's the tragedy,' he said.

'I like every one of these people. Bill may not believe it today. But I like Bill. I don't know what Bill was like 30 years ago. I don't know what Bill's like as a father or a husband. I respect him for the way he has dealt with me. I also like Ira Keeshin and I also like Jean McGothlin,' he said.

The row over the book is not the first controversy in McGinniss' writing career. In 1988, he was sued after producing Fatal Vision, a true-crime thriller about Green Beret doctor Jeffrey MacDonald, who was convicted of stabbing his wife and two daughters to death. MacDonald argued that the author pretended to believe he was innocent to win his trust before portraying him as a murderous sociopath in the book. The parties eventually reached an out-of-court settlement for an undisclosed amount.

In her book The Journalist and the Murderer, Janet Malcolm used the McGinniss-MacDonald trial to explore the problematic relationship and the ethical issues between journalists and their subjects.

After the 1993 publication of The Last Brother, a biography of Senator Edward Kennedy, McGinniss was accused of plagiarism and of conjuring passages that are presented as the thoughts and quotes of Kennedy, who he had never interviewed. But McGinniss argued that he was the victim of a conspiracy by the Kennedy family to destroy his book and deflect criticism of the senator, who is portrayed as a failed member of a family that demands greatness.

After those episodes, McGinniss turned his attention to more palatable subject matters, such as soccer in Italy and a race season in Saratoga.

'Do readers like to read happy stories? I don't think so,' McGinniss said. 'But I want to write happy stories for the rest of my life.'