SAN FRANCISCO -- A San Francisco sheriff's deputy's gun was stolen from a parked rental car Sunday, sheriff's officials said Monday.
Sheriff Vicki Hennessy said the deputy, who was off-duty at the time of the theft, reported the department-issued weapon stolen to the San Francisco Police Department around 6:30 p.m.
The gun was apparently stored in the trunk of a rental car parked in San Francisco.
"Preliminary information indicates the firearm was stored in violation of our policy," Hennessy said. "Our department policy mandates that a firearm stored in a vehicle be stored in a metal or composite lockbox that is affixed to the interior of the vehicle and out of public view."
The department has opened an investigation into the theft and Hennessey said she was taking the matter "extremely seriously."
The weapon has not been recovered.
Guns stolen from law enforcement have been used in several fatal shootings in recent years.
San Francisco police reported last week that a gun stolen from an officer's personal vehicle on Aug. 12 was used in an alleged crime spree over the next several days, including the fatal shooting of 23-year-old Abel Enrique Esquivel Jr., on Aug. 15 in the city's Mission District.
Three people have been arrested in connection with that shooting, which allegedly occurred during a robbery.
A gun stolen from a U.S. Bureau of Land Management agent was also used in the fatal shooting of 32-year-old Kate Steinle in July 2015 in San Francisco. Jose Ines Garcia-Zarate, 54, is expected to stand trial on a murder charge in that case later this fall.
And in Oakland, 27-year-old Antonio Ramos was shot and killed on Sept. 29, 2015, with a gun that had been stolen from an Immigration and Customs Enforcement agent's car weeks earlier. Police arrested 20-year-old Marquise Holloway in connection with the shooting on Nov. 20.
In response to those and other incidents, a state law was signed last year requiring that law enforcement officers store guns in a locked trunk or safe box if they are kept in a vehicle. Civilians were already required to store their weapons securely but law enforcement had previously been exempt.
The San Francisco Board of Supervisors also passed an ordinance in February 2016 requiring all weapons left in vehicles to be secured in a locked trunk or lock box, for both civilians and law enforcement.
San Francisco sheriff's deputy's gun stolen from parked rental car