SAN FRANCISCO » A defense attorney for a man charged with murder and racketeering in a Chinatown organized crime investigation told jurors that prosecutors had not proven their allegations and that a conviction would send an innocent man to prison.

J. Tony Serra, lead attorney for Raymond “Shrimp Boy” Chow, is expected to continue his closing argument Tuesday in a two-month trial that has riveted the country for its colorful characters and alleged crimes.

The investigation, led by an undercover federal agent posing as a member of an East Coast crime syndicate, had previously ensnared a state senator. Serra is a flamboyant and well-known defense lawyer. And in an unusual move, Chow took to the stand to testify he had renounced his life of crime and declare his innocence.

Prosecutors have said Chow took over a Chinese fraternal group with criminal ties after having its previous leader killed and ran an enterprise that engaged in drug trafficking, money laundering and the sale of stolen cigarettes and alcohol. He is also accused in a second killing.

On Monday, Serra derided the prosecution’s evidence as flimsy, based on secret recordings and shady testimony from Chow’s former colleagues. He railed at the government use of secret surveillance.

“If you convict this man on the nature and quality of the evidence that has been produced, you will be convicting an innocent person,” Serra said, later adding: “This is a case that is fraught, fraught with reasonable doubt.”

Much of Monday’s trial in the courtroom of U.S. District Judge Charles Breyer was consumed by a lengthy closing argument by the prosecution. Assistant U.S. Attorney Susan Badger asked jurors to disregard claims that Chow was a changed man, saying that deception was his true nature.

“He is not the victim here,” Badger said during her nearly four-hour presentation. “He is not the world’s most misunderstood criminal.”

She pointed to an evidence table displaying about a dozen firearms, guns seized from the homes of Chow’s alleged partners in crime.

The 56-year-old Chow sat at a table flanked by four of his attorneys. He looked on stoically for the most part, aided by a language interpreter. At one point, he cheerily waved hello to a person in the courtroom audience.

After Serra concludes his closing Tuesday, prosecutors will get a chance to rebut. Jurors should get the case Tuesday.

The multi-year investigation was spearheaded by an undercover FBI agent who testified that he spent hours with Chow and people connected to him at fancy restaurants and nightclubs, recording many of their conversations.

The agent, who testified under a pseudonym to protect his identity, said Chow tried to distance himself from any criminal activity during the probe but repeatedly accepted money after introducing the agent to money launderers.

The probe led to the indictment of more than two dozen people in 2014 and the subsequent racketeering conviction of state Sen. Leland Yee.

Chow testified to dealing drugs and getting involved in a street gang but said he decided to renounce criminal activity after engaging in meditation.

He denied involvement in the slayings and said the agent gave him the money because the agent was looking out for him, not in exchange for criminal activity.