Mongols biker who killed cop during raid agrees to manslaughter plea after 2 murder acquittals

A man behind bars in a courtroom
David Martinez appears in court in 2014. At two trials, he insisted that he did not know it was SWAT officers raiding his home in October 2014 when he fired a shotgun, saying he believed it was Mongols coming for him.
(Irfan Khan / Los Angeles Times)

A member of the Mongols motorcycle gang who killed a Pomona police SWAT officer serving a search warrant more than eight years ago pleaded no contest Wednesday to voluntary manslaughter after twice being acquitted of murder.

David Martinez, 44, had been found not guilty of first-degree murder and second-degree murder in two separate trials over the fatal shooting of Officer Shaun Diamond during the October 2014 raid on his San Gabriel family home.

Martinez insisted he did not know it was the police making a forced entry to his home when he fired a shotgun once, telling one of the juries he believed it was members of the Mongols biker gang coming for him.


Last month, jurors in the most recent trial deadlocked on two lesser charges of voluntary manslaughter and assault with a firearm on a police officer. On Wednesday, Martinez opted to plead no contest to both charges. He is slated to be sentenced Jan. 17.

After nearly two months of testimony and deliberation, a Los Angeles Superior court judge on Friday declared a mistrial in the murder trial of a Mongols Motorcycle Club member after a jury deadlocked over whether he acted in self-defense when he fatally shot Pomona police SWAT officer Shaun Diamond in 2014.

June 29, 2019

Martinez’s open plea to the court means he has not made a deal with prosecutors on sentencing. Having served more than eight years, his lawyers are hoping he will be released given the time served. But the prosecutor is expected to seek a higher sentence.

Diamond, 45, was a 16-year law enforcement veteran who had also worked for the Los Angeles and Montebello police departments. The gunfire on Oct. 28, 2014, severed his spine and shattered his jaw, and he died after a day on life support at Pasadena’s Huntington Memorial Hospital.

The officer was part of a multi-agency operation targeting the Mongols with several warrants.

Martinez’s home had a metal screen door and a wooden front door; when a knock on the door got no response, an entry team breached the screen door. Diamond along with a second officer used a tool to force open the door.

The ruling comes nearly a year after the Mongols’ attorney filed a motion for a new trial, claiming the club’s president had acted as a federal informant.

Oct. 11, 2022

According to the San Gabriel Valley Tribune, Martinez testified at trial that after going to bed around 3 a.m. he felt the window shake and thought it was his father getting up to go to work. He then heard a banging sound, grabbed a shotgun by the side of his bed and went to the front door. He said he didn’t hear the SWAT officers saying “search warrant” or “police.”


During the latest trial, his lawyer said Martinez had wanted to quit the Mongol motorcycle club and believed it was fellow Mongols at the door of his parents’ home that morning, so he fired a 24-gauge shotgun to defend his family.

Prosecutors, however, said Martinez never left the Mongols and had kept all his tattoos and continued to communicate with Mongols. They noted that Martinez tested positive for methamphetamine the day of the shooting.