Jin Zhongqi was found dead a week after the double killing, in what appeared to be a suicide, according to the Beijing Times newspaper, an affiliate of Communist Party mouthpiece People's Daily.
Jin, 59, helped house homeless petitioners, people who travel to the capital in an effort to get central authorities to right local government malfeasance.
On June 27, Jin got into an argument over a ‘toe stepping incident’ with passengers on a bus, the Beijing Times cited eyewitnesses as saying.
After alighting he allegedly fatally stabbed two people and injured a third, before fleeing on foot, it added.
Police issued a wanted notice for him, offering a 50,000 yuan ($7,500) reward.
Ahead of the killings Jin -- who had previously been put under house arrest -- posted photos on social media of people on a bus, saying they were state security agents who were following him, fellow activist Dong Jiqin told AFP.
‘Jin said before that security agents would stop him from using public transport sometimes, they would interfere with his daily life,’ Dong said, adding he had not seen him in about six months.
‘He was a good man who helped other people in the community of human rights advocates,’ Dong told AFP.
Jin had previously served a 12 year prison sentence, according to Dong.
China's President Xi Jinping has overseen a crackdown on dissent since coming to power in 2012, with hundreds of lawyers, activists and academics detained and dozens jailed.
Police in Beijing did not answer questions faxed to them by AFP about the identities of the victims and the circumstances of Jin's suicide.
