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2 SF police officers arrested on suspicion of destroying evidence, retired officer also booked on gun charge

A San Francisco police SUV is parked outside a storefront adorned with a Christmas tree.
A police vehicle sits parked at Union Square on Nov. 22, 2021.

Two San Francisco police officers who allegedly destroyed evidence and a third retired officer who is accused of being in possession of an illegal firearm were arrested Tuesday in connection with a pair of unrelated incidents.

Officers Kevin Lyons and Kevin Sien are facing misdemeanor charges for allegedly destroying evidence after responding last July to a Marriott hotel in the South of Market area, where security found suspected methamphetamine as well as possibly stolen credit cards and IDs.

Both officers dumped the documents and Lyons flushed the drugs down a toilet instead of booking the items into evidence, according to the District Attorney’s Office. The officers were both transferred to nonpublic contact positions before being cited and released Tuesday, police said.

Separately, retired Officer Mark Williams was working part-time at the department’s property control room last August when police discovered that a machine gun was missing, police and prosecutors said. An investigation later determined that Williams took the MP5SD submachine gun and had it at his home in Napa.

Williams was fired by the department and booked Tuesday on felony charges of possession of a machine gun, possession of a silencer and embezzlement. He was immediately released from custody, according to his attorney.

Police Chief Bill Scott called the officers’ actions illegal and disappointing in a statement announcing the arrests Tuesday. At the same time, Scott said the fact that the charges resulted from internal investigations by his department reaffirms “the principle that no one—including a current or retired police officer—is above the law.” 

In a statement, District Attorney Chesa Boudin said Lyons and Sien “undermined their own colleagues, my office, and our criminal justice system as a whole by destroying and concealing the evidence of a crime, simply because they didn’t want to take the time to do their jobs.”

Boudin also said Williams “breached the trust and safety of our community when he removed the machine gun from SFPD’s custody.”

Lyons is a 21-year veteran of the San Francisco Police Department who ran for vice president of the police union in 2019. Sien is a five-year veteran. Both were assigned to the Tenderloin Station at the time of the incident and later transferred.

Williams was assigned to the Tactical Unit before his retirement in 2017. 

Tracy McCray, acting president of the San Francisco Police Officers Association, said the union is providing legal representation for Lyons and Sien.

“It’s an unfortunate situation that our members find themselves in, but we have full confidence that the facts will come out on the side of our members,” McCray said.

Sien’s attorney, Christopher Shea, said the officer took a “shortcut” by helping dump the documents in a shred bin instead of booking them into evidence. 

“That’s bad police work but it’s not criminal,” Shea said, adding that Sien should face internal discipline, not criminal consequences. “He is willing to accept responsibility for any administrative consequences.”

Tony Brass, an attorney for Williams, said his client only “borrowed” the gun from the property control room and “had every intention of returning it.” Brass said the gun was missing a magazine and that Williams did not intend to use it.

“He simply took it home and put it in his safe,” Brass said, adding that Williams is “appropriately remorseful.”

“He realizes that it was a very, very bad decision,” he said.

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