The defendant at the center of an organized crime investigation in San Francisco's Chinatown acknowledged his criminal past during testimony Monday, but said law enforcement hounded him after he tried to go straight and got jobs.

Raymond "Shrimp Boy" Chow took the stand for the first time in the racketeering, money laundering and murder trial against him in federal court.

Prosecutors say Chow took over a Chinese fraternal group with criminal ties after having its previous leader killed and ran a racketeering enterprise that engaged in drug trafficking, money laundering and the sale of stolen cigarettes and alcohol.

The multi-year investigation included an undercover FBI agent posing as a member of an East Coast crime syndicate and led to the conviction of a state senator.

Chow appeared relaxed as he testified in a maroon suit under questioning from his attorney.

He said he ran an escort service, dealt cocaine and was involved in a street gang, but upon his release from prison in 1989 for a second time, he got jobs at a supermarket and law office. That did not last, however, as he continued to face scrutiny from police, he said. San Francisco police talked to his employers, and the FBI picked him up on suspicion of involvement in a jewelry heist.

Chow testified in English, though it's not his first language and he has used a translator during other court hearings. His attorney said during opening statements he wanted the jury to hear that Chow doesn't always understand English and that his diction and tenses are not always used correctly.

"I try very hard to stay out, to not be the criminal at the time," Chow said during testimony.

Chow was convicted on a federal gun charge in 1995 and released in 2003 after agreeing to cooperate in another prosecution. He said prosecutors reneged on promises to put him in witness protection.

An undercover agent, who testified earlier under the pseudonym David Jordan to protect his identify, said Chow tried to distance himself from any criminal activity during the probe. But, the agent said, Chow repeatedly accepted money after introducing the agent to money launderers.

The agent spent hours with Chow and people connected to him at fancy restaurants and nightclubs, recording many of their conversations as he built a case. That case ultimately led to charges against Chow and more than two dozen others in 2014 and the conviction of state Sen. Leland Yee, who pleaded guilty to racketeering in July.

Chow's attorneys say the FBI agent instigated the crimes for which people were later arrested and forced money on him, often when Chow was drunk. They say Chow had turned his life around and reformed.