SAN FRANCISCO » The defendant at the center of an organized crime investigation in San Francisco’s Chinatown acknowledged dealing drugs and getting involved in a street gang during testimony today, but said he later renounced criminal activity and had nothing to do with a 2006 murder.

Raymond “Shrimp Boy” Chow took the stand for the first time in the racketeering and murder trial against him in federal court.

Prosecutors say Chow had Allen Leung, the leader of a Chinese fraternal group with criminal ties, killed and that Chow then took over the group. Chow then ran an enterprise that engaged in drug trafficking, money laundering and the sale of stolen cigarettes and alcohol, according to prosecutors.

The lengthy investigation included an undercover FBI agent posing as a member of an East Coast crime syndicate. It led to the indictment of more than two dozen people and the conviction of a state senator.

Chow appeared relaxed as he testified in a maroon blazer 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.

Prosecutors have played numerous recordings of Chow’s conversations with the undercover agent as evidence.

Chow was convicted on a federal gun charge in 1995 and released in 2003 after agreeing to cooperate in another prosecution. He said after engaging in meditation, he decided to renounce criminal activity and focused instead on writing his biography.

“I change myself,” he said. “I tell myself I’m not going to cross the line and commit the crime.”

Chow later said there were rumors in Chinatown that he had killed Leung, but that he was not involved in the slaying.

“I’ve been waiting for this chance in court to tell everybody I do not kill Allen Leung,” Chow said, his voice rising. “I am innocent on that. That’s a fact.”

The 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.

Prosecutors Monday frequently objected to Chow’s long, narrative responses to questions, arguing they were not relevant to the case. Chow was set to continue testifying on Tuesday.