He "was unaware that his brother had purchased the revolver used in this incident on Sept. 16, 2016," from a gun store in Pacifica, according to the district attorney's report.
"All available evidence supports the conclusion that Officers Dominguez and Chew acted in self-defense and in defense of others when they fired their weapons at McWherter," the report says. "Under California law, the officers were justified in using deadly force because they faced an imminent danger to themselves and to others."
Downs, the officer originally shot by McWherter, recently told the Marin Independent Journal that he is "pretty much back to being 100 percent physically,” has returned to modified duty and hopes to be back to full duty by the end of the year.
The oldest of the shooting investigations cleared by the district attorney's office involves the death on Sept. 25, 2014, of Giovany Contreras-Sandoval in the Financial District. Contreras-Sandoval, a Richmond resident, was shot following a pursuit from the East Bay prompted by a report of a carjacking.
After a crash at California and Battery streets, civilian witnesses told officers that Contreras-Sandoval had a gun and had fired at least one shot before police arrived, according to the report.
When officers approached the vehicle, Contreras-Sandoval refused to put down his gun and instead raised it toward both a group of officers and civilians in the area, the report said. The officers fired in self-defense, the report concludes.
The district attorney's office also issued a decision today in a non-injury shooting that occurred on May 21 of this year after officers responded to a report of an armed robbery at a home in the 2100 block of Quesada Avenue.
When officers encountered three robbery suspects leaving the house, one of the suspects fired at least five rounds at them.
Officer Dack Thompson fired a single shot at the suspect, but no one was injured in the gunfire, the report notes. The district attorney's office found Thompson acted in self-defense and defense of others.
All three investigations were conducted by the Independent Investigations Bureau of the district attorney's office. The Police Department also investigates police shootings and conducts administrative investigations after the district attorney's office completes its criminal review.
The decisions issued Thursday will chip away at a backlog of police shooting investigations in the district attorney's office.
According to a 2016 civil grand jury report, the reports can take an average of 20 months to complete.
Prior to today, the last decision in an officer-involved shooting investigation came in April of this year, when the district attorney's office found the Feb. 26, 2015, Mission District shooting of 21-year-old Amilcar Perez-Lopez was legally justified.
A number of other investigations into fatal police shootings remain unresolved, including the controversial shootings of Mario Woods in 2015 and those of Luis Gongora and Jessica Williams in 2016.
In all, the district attorney's office appears to have 10 pending investigations into fatal police shootings since 2014, with the oldest being that of O'Shaine Evans, who was shot on Oct. 7, 2014.
Police have fatally shot two people this year, Nicholas Flusche, 26, on May 3, and Damian Murray, 46, on Sept. 24. In addition, officers shot and injured Sean Moore on Jan. 6, but Moore survived his injuries and ultimately saw all charges dropped against him in connection with that case.
This post contains reporting from Bay City News Service.