A letter addressed to US President Barack Obama suspected of containing the deadly poison ricin was intercepted at a mail-screening facility outside the White House yesterday, as China mourned the death of a mainland graduate student in the Boston Marathon bombing.
The interception of the Obama letter came a day after another screening site intercepted a ricin-tainted letter bound for the office of Senator Roger Wicker.
While the FBI said investigations had not found a link between the letters and the Boston attack, their discovery increased tension two days after twin bombs killed three people and injured more than 170.
Among the dead was a mainland student studying at Boston University, who was described by shocked friends as a girl dedicated to her work.
The Chinese consulate in New York and Boston University confirmed a graduate student had been killed, but did not disclose personal details. However, mainland internet users identified her as Dorothy Lu Lingzi , who went to Boston University last year for a master's programme in mathematics and statistics.
President Xi Jinping offered condolences to the victims and ordered Chinese diplomatic missions in the US to offer assistance, Xinhua reported.
Lu's last microblog entry was posted on Monday with a picture of a bowl of Chinese fried bread and a tweet that said: "My wonderful breakfast." More than 200,000 condolence messages were posted on the entry.
"I had not thought that this would be your last breakfast," read one. Another said: "May you rest in peace."
Lu went to watch the marathon with two friends, Qian Tingting and Zhou Danling . Zhou, from Sichuan province, was hurt in the blast and wrote a note that said "I am fine, don't worry" after having two operations at Boston Medical Centre. Qian was uninjured.
As Lu was mourned, authorities recovered a piece of circuit board they believed was part of one of the devices and found the lid of a pressure cooker that contained one of the bombs on the roof of a nearby building.
But as FBI agents zeroed in on how the bombings were carried out, they still did not know who did it and why.
Zhang Shuo , a teacher of Lu in an overseas education preparation class, said: "She was a smart student and dedicated to her work."
Lu got a degree in international economics and trade at the Beijing Institute of Technology and went to Northeast Yucai School in Shenyang .
She excelled in mathematics and had worked as an intern and assistant in financial institutions as well as Deloitte Consulting.
Additional reporting by Bloomberg, Associated Press