DALLAS — A Houston transit police officer resigned this week following the release of a surveillance video that shows him using a baton to repeatedly strike a man he found slumped on a seat on a rail platform.

An internal review recommended Officer Jairus Warren’s dismissal for using excessive force in the Sept. 14 beating of Darrell Giles, who is black. Authorities said Warren quit Monday.

Giles, 31, was arrested on charges of trespassing and resisting arrest, but the charges were later dropped. Surveillance video released by Metropolitan Transit Authority police showed Warren, who is also black, striking Giles 15 times with his baton.

A second officer present during the beating, Daniel Reynoso, was suspended but later cleared of wrongdoing, transit police Chief Vera Bumpers said Monday. Reynoso will return to work and undergo additional training, she said.

The Harris County district attorney’s office is reviewing the matter and will decide whether charges are filed against Warren, Bumpers said.

“I did not count the number of times that Mr. Giles was struck but one is too many, in my opinion, if it’s not justified,” she said during a news conference.

The video, which had no accompanying audio, shows Giles slumped on the seat, apparently sleeping. Warren and Reynoso approach to wake him. Warren appears to motion for Giles to stand and when he doesn’t the officer kicks his foot. Giles, who according to court records is 6-foot-3 and 285 lbs., immediately stands and steps toward Warren, who responds by striking him repeatedly.

Giles was taken into custody and then treated at a hospital after complaining of arm pain, Bumpers said. Warren joined the force in November and Bumpers said he had never faced a complaint of using excessive force.

Giles’ mother, Ossie Giles, told KPRC-TV that her son can only be accused of sleeping at a train stop.

“It still hurt(s) my heart every time I see it, that they beat my child like that,” she said.

Eight days after the incident, Giles was arrested on a charge of assaulting a public servant, according to court records. He was taken into custody for fighting in public and later became combative with officers, eventually biting one on the arm, Houston police spokesman Kese Smith said. An attorney listed in court records as representing Giles in the most recent case did not return a phone message seeking comment.

Ashton P. Woods, an organizer for Black Lives Matter in Houston, commended Bumpers for reaching out to his group to discuss the case and for releasing the surveillance video. BLM had initially called for a federal investigation.

“They responded with transparency and serve as an example of how other police agencies can respond,” Woods said of transit police.

Follow David Warren on Twitter at https://twitter.com/WarrenJourno