A sheriff’s deputy who shot and killed an unarmed black man who was in an apparent mental health crisis has been fired.

Harris County sheriff Ed Gonzalez sacked Cameron Brewer on Friday after a departmental disciplinary committee recommended that the 44-year-old lose his job for killing Danny Ray Thomas on a north Houston street on the afternoon of 22 March.

The department said in a news release that Brewer, who is also black, had failed to follow its use of force policy according to the findings of an internal investigation.

Thomas was walking with his trousers around his ankles and had just been in an altercation with another man when Brewer encountered him. Dashcam footage from Brewer’s car and cellphone video from a bystander do not capture the moment a single shot is fired into the 35-year-old’s chest but show him walking towards the officer, who yells: “I’ll shoot your ass, man! Get down on the ground!”

Brewer, who was equipped with a Taser but did not use it, shot Thomas within 30 seconds of arriving on the scene. Gonzalez told reporters last month it was “concerning” that the officer went directly to lethal force without attempting de-escalation techniques.

The Harris County deputies’ organization, representing Brewer, criticised the firing.

“Sheriff Gonzalez has second-guessed Deputy Brewer’s split-second decision … to use deadly force to protect himself,” it said in a statement. Brewer declined to comment to ABC13 local news.

Evidence is expected to be presented by the Harris County district attorney’s office to a grand jury, which will decide whether to indict Brewer on criminal charges.

Thomas’ family have filed a civil wrongful death lawsuit against the officer and the county. Another investigation, by the Houston police department, is continuing.

“You have a Taser you could have reached for,” said Dieter Cantu, lead criminal justice organiser with the Texas Organizing Project activist group, during a protest last month at the shooting site. “The guy had his pants down, you could have restrained him. You could have done a lot of other options beside shooting.”

Thomas died four days after police in Sacramento, California, fatally shot an unarmed African American man, Stephon Clark, prompting a series of protests. “It’s old. It’s getting tiring – black and brown communities, that’s who it’s happening to, over and over,” Cantu said.

Thomas’s family has said he was left traumatised after two of his children were drowned in a bathtub in 2016, allegedly by their mother.

Ben Crump and Bob Hilliard, attorneys for the family, said in a statement on Saturday: “The acknowledgment that this officer violated use of force policy when he killed a nonthreatening innocent man who was mentally ill and who was committing no crime will enrage a Harris County jury.

“Perhaps a jury’s verdict will cause the sheriff’s department to focus on training, supervision and monitoring its officers. The colour of your skin and state of your mental health should not be factors in whether you live or die in an interaction with police.”