The deputy was not wearing his newly issued body camera, so what happened next was not captured in the video released by the sheriff’s office. But the sound of a single gunshot could be heard, and Mr. Thomas was pronounced dead at a hospital.

Deputy Brewer, who joined the sheriff’s department in 2016, was placed on administrative duty after the shooting, pending an internal affairs investigation. In its statement on Friday, the department said that Mr. Thomas was “behaving erratically” but that he was unarmed. Although Deputy Brewer was carrying a Taser, he did not use it before shooting Mr. Thomas, Sheriff Ed Gonzalez has said.

“The brave men and women of the Harris County Sheriff’s Office are called upon to make life-or-death decisions on a daily basis, and we take that responsibility very seriously,” Sheriff Gonzalez said in the statement. “We hold the community’s trust as sacred, and we will continue to support our deputies with clear policies and the valuable training they need to protect the lives of all our residents.”

Deputy Brewer did not respond to a phone call seeking comment on Friday. A spokeswoman for the Houston Police Department said on Friday that the department was still investigating the shooting.

The Harris County Deputies’ Organization expressed condolences to Mr. Thomas’s family but said in a statement that it stood behind Deputy Brewer. “Sheriff Gonzalez has second-guessed Deputy Brewer’s split-second decision,” it said. “We do not agree with the decision of Sheriff Gonzalez to terminate Deputy Brewer.”