"I don't understand why they didn't want to stay on the scene, talk to police and testify against their attackers," he said. "They should have done the right thing."
Without witnesses or victims, Wu's heroics have often been dismissed as personal disputes played out in street fights.
Good deeds not recognized
"Why is society like this?" he asked. "I had hoped there was more righteousness in the city. I wish there are more people like me who take street crime seriously."
In March, Wu was fired from his job in a restaurant, got drunk and decided to take his own life by jumping into the Huangpu River. He was saved by a church pastor and police as he hung from the rails of a flood-control wall on the Bund.
"Wu did a lot of good things that should have helped his self-esteem, but instead he was depressed because his good deeds weren't recognized by the authorities or the public," said Pastor Wang, of a local church. "He was lost in his own world of catching thieves. He couldn't see his self-worth. He needed to find himself."
After hitting bottom, Wu's life began to turn toward the better. He started medical treatment and got jobs as a salesman and waiter. But they never lasted long. With only a middle-school education, his employment opportunities have been limited. He said he wants to enter a job-skills training program and possibly become an electrician.
"I don't care too much about money as long as I have a steady income," Wu said.
Left unsaid is the impression that Wu's obsession with foiling pickpockets helped turn him into a social misfit who finds it hard to mix with other people or fit into workplaces.
Job interview for airline stewards