A gunman killed three people outside of a Target store in Austin, Texas, on Monday afternoon, then stole a succession of cars before he was apprehended, local police officials said.

Two of the victims were pronounced dead at the scene, shortly after emergency responders arrived around 2:20 p.m. Central time. A third person died at a nearby hospital, and a fourth was injured.

Police said the gunman, a 32-year-old man, then hijacked a car, crashed it, and stole another car. Austin police officers found him in South Austin and took him into custody after shocking him with a stun gun.

The man, whose name has not been released, had a history of mental health problems and has previously been placed on emergency holds, according to Lisa Davis, chief of the Austin Police Department. Such holds typically occur when individuals face a mental health crisis and pose a risk to themselves or others.

“This is a very sad day for Austin, a very sad day for all,” Ms. Davis said.

Authorities said they did not know the motive for the attack.

In a statement on social media, Austin’s mayor, Kirk Watson, said an investigation was ongoing.

“What I’ll say is that this was a sickening, cowardly act of violence,” Mr. Watson wrote.