The gun, a personal firearm registered to the officer, was stolen from the officer's personal vehicle on Aug. 12, police said this afternoon.
Three days later, around 2 a.m. on Aug. 15th, 23-year-old Abel Enrique Esquivel, Jr. was shot as he stood near the intersection of 26th Street and South Van Ness Avenue.
He was taken to San Francisco General Hospital but died the following day.
Police arrested three suspects in connection with Esquivel's murder this week. Erick Garcia Pineda, an 18-year-old San Francisco resident and Jesus Perez-Araujo, a 24-year-old San Francisco resident, were arrested on Monday in the area of 16th and Mission streets, and Daniel Cruz, an 18-year-old San Francisco resident, was arrested Tuesday in the 2600 block of Mission Street.
Pineda was arrested on suspicion of murder, robbery, conspiracy, burglary and attempted murder, Perez-Araujo on robbery, burglary and conspiracy and Cruz on murder, conspiracy, robbery and possession of stolen property.
In the course of the investigation, police discovered the link between the gun used in the homicide and the police officer. An internal investigation is now underway into the circumstances surrounding the weapon's theft, police said.
The San Francisco Police Officer's Association issued a statement this afternoon saying the officer did not realize that the weapon had been stolen.
"There were no visible signs of the burglary, and the officer did not realize that the vehicle had been broken into, nor that the firearm had been stolen," the statement said.
"The officer, a highly-decorated veteran, is devastated," the SFPOA statement said. "He is working with the department to fully comply with its investigation into this case."
Police said they believe the three suspects in the case were also responsible for several robberies that occurred in the Mission District between Aug. 13 and Aug. 15, as well as an aggravated assault that occurred around 2:17 a.m. on the 2600 block of Mission Street shortly after Esquivel was shot.
Police did not indicate whether the officer's gun was also used in those incidents or whether the weapon has been recovered.