He said that a man who had raised Mr. McKnight used to work as a deputy in the sheriff’s office and that some employees were “close with his family.” It was not immediately clear to whom he was referring; a 2007 profile in The Los Angeles Times said McKnight was raised by his mother, Jennifer McKnight.

Sheriff Normand disputed several rumors that had spread on social media, including that Mr. Gasser had stood over Mr. McKnight as he fired the gun, that a video has been recovered and that a witness had said Mr. McKnight apologized to Mr. Gasser before the shooting.

All of those are false, he said, and he advised people to believe only what they heard from officials like himself and the district attorney. “I strongly suggest you stop believing what you’re reading,” he said.

Councilman Mark Spears, who also spoke at the news conference, said: “It shouldn’t be a rush to judgment. The facts are still coming out, and we should base it on facts, not on Facebook and other social media.” He also said officials were “praying” for the McKnight family.

In a statement released before the news conference, the sheriff’s office said that Mr. Gasser had handed over a semiautomatic handgun to officers at the scene. The sheriff said at the news conference that Mr. Gasser had fired three rounds from inside his vehicle.

At a news conference, local N.A.A.C.P. officials criticized the authorities for releasing Mr. Gasser, pledging to demonstrate peacefully.