NEW YORK (NYTIMES) - A Queens lawyer held a meeting with a young client last week that ended in chaos.

The client, Xiaoning Zhang, 25, grew furious after the lawyer, Mr Jim Li, told her he would stop working with her, according to Mr Li's friends and colleagues.

She threatened him, causing such a commotion that the police were called. But Mr Li, 66, asked that they not arrest her.

Then, on Monday (March 14) morning, Zhang returned to the law office armed with two knives. According to the police and witnesses, she stabbed Mr Li in the chest and neck, killing a man best known as a key participant in the pro-democracy protests at Tiananmen Square in 1989.

Zhang has been arrested and charged by the police with murder.

Neither she nor a lawyer representing her could be reached Tuesday.

Mr Li, born Li Jinjin, was a doctoral student in constitutional law at Beijing University during the Tiananmen Square demonstrations and became a legal adviser to a Beijing union that played a key role in the protests.

After the Chinese government cracked down on the demonstrations, Mr Li escaped to his home in Wuhan.

But the authorities found him there, arresting him in the middle of the night in front of his family, including his young son, he later told a Newsday reporter.

He was held for nearly two years at Qincheng Prison, along with many other political prisoners.

After his 1991 release, he emigrated to the United States, studying at Columbia University for a year and then completing his doctorate at the University of Wisconsin Law School.

He returned to New York, where he worked as an immigration lawyer. He remained a pro-democracy activist and dreamed of returning to China to help shape the country's future, according to the interview with Newsday.

The lawyer's friends and colleagues were stunned by the attack.

"He was a tireless fighter and advocate for democracy, and he was a great American," said Mr Aaron Lebenger, a colleague who had known Mr Li for more than 20 years.

Mr Wayne Zhu, an immigration lawyer and a close friend, said that Mr Li "always had a good heart".

Mr Zhu said that Zhang had told his friend that she had been persecuted in Beijing, saying she had been detained and sexually assaulted by the police.

Mr Chris Li, who worked with Mr Jim Li, said that their law firm had been working with Zhang pro bono, and that she had visited the office Friday asking that Jim Li try to get a picture of her protesting in front of the United Nations building removed from the Internet.

When Mr Li told her that he could not, she grew irate, Mr Chris Li said. She then told Mr Jim Li that everything in her asylum declaration was fabricated.

After that, Mr Li told her he would no longer represent her. When she threatened him and attempted to choke him, he called the police.

The police confirmed that they came to the office shortly before 5pm Friday to respond to an "emotionally disturbed person," that there was a dispute in the office and that no arrests had been made.

On Monday morning, Zhang returned to the law office shortly after Mr Jim Li arrived, bringing a cake to the front desk and telling employees there that she was grateful to them, Mr Chris Li said.

She accompanied Mr Jim Li into his office, and employees soon heard screaming.

Mr Chris Li said that when he entered the office, Mr Jim Li was bleeding from the neck and the abdomen and Zhang was standing behind him.

Mr Li was a doctoral student in 1989 when the Tiananmen Square protests began with thousands demonstrating against the Chinese Communist Party, criticising corruption and calling for democratic freedoms.

He served as a legal adviser to the Beijing Workers Autonomous Federation, the key organisation of workers that aligned itself with the students.

He was interrogated a number of times while detained at Qincheng Prison, but told friends and colleagues that he had never cooperated.

In the US, after his studies at Columbia, he initially struggled, telling a newspaper at the time that he was unable to find work in a law firm because of his shaky English. He considered working in a restaurant.

But soon afterwards, he was able to attend the law school at the University of Wisconsin, where he became a fan of the Green Bay Packers.

In New York, he helped clients gain admission to the United States and devoted himself to pro-democracy programmes, his friends said.

He was one of the lawyers who represented Zhou Yongjun, a student leader in the Tiananmen Square movement who was detained by the Chinese authorities in 2008 and charged with fraud.

He fought against the Chinese government's practice of using Interpol red notices to apprehend political opponents. And he worked with many clients, including Zhang, pro bono, Mr Zhu and Mr Lebenger said.

"He helped a lot of Chinese people who had the experience of being persecuted by the Chinese government," Mr Gu said.