By Dakin Andone and Artemis Moshtaghian, CNN

(CNN) -- Authorities in Houston are investigating an incident in which a man was fatally shot by a sheriff's deputy last week at a busy intersection.

Cell phone video obtained by CNN affiliate KPRC shows Danny Ray Thomas, with his pants around his ankles, approaching the Harris County Sheriff's Office deputy, who is backing away with his gun pointed at Thomas' chest.

The video is jumpy and doesn't show what happens next. But moments later it shows Thomas lying prone in the street as the deputy attends to him.

Thomas, 34, died last Thursday from a single gunshot wound.

Markeeta Thomas, Danny's sister, told KPRC she didn't believe the deputy needed to use lethal force against her brother.

"You clearly could have Tased him," she said, her voice thick with tears. "He wasn't trying to shoot you. He wasn't trying to do anything."

Police: Thomas ignored officer's commands

CNN has reached out to police but so far has been unable to determine whether Thomas was armed. A Harris County Sheriff's Office spokesman told the Houston Chronicle that no weapon was recovered.

Because the shooting occurred in the jurisdiction of the Houston Police Department, that agency will conduct a joint investigation with the district attorney's Office, said Harris County Sheriff Ed Gonzalez.

Police said in a press release that witnesses saw Thomas in the intersection with his pants around his ankles about 1 p.m. Thursday, while "talking to himself and hitting vehicles as they passed by."

Thomas hit a white vehicle, police said, prompting an altercation between himself and the driver. The deputy, who has not been named, saw the altercation from his squad car as he drove up to the intersection, the release said.

He exited his car and ordered Thomas to stop, the news release said. According to police, Thomas ignored the commands.

"Fearing for his safety, the deputy discharged his duty weapon, striking Thomas once in the chest," the police statement said. Thomas was taken to a hospital where he was later pronounced dead, Gonzalez told reporters.

Sister: Thomas was struggling after his children died

"Our condolences go to the family of this individual," Gonzalez said during a Thursday press conference at the scene.

"Obviously they're someone's loved one. These situations are always difficult, and so the main thing we can do is to get the facts and that we're thorough and transparent."

Markeeta Thomas said the video appears to show her brother was not in his right mind, KPRC reported. Thomas, she said, has been dealing with a family tragedy. His wife, Sheborah Thomas, was charged in 2016 in the drowning their two children, ages 7 and 5, in a bathtub.

"Whenever he got into that mind frame," Markeeta Thomas said, "thinking about his wife and his kids, he just felt like he was alone."