Investigators searched for clues on Sunday following the ambush-style killing of a Los Angeles County sheriff’s deputy, as outpourings of grief flowed over the officer’s dedication to public service.

The deputy, Ryan Clinkunbroomer, 30, was found unconscious, with a gunshot wound to the head, by a passer-by on Saturday evening, the Los Angeles County Sheriff’s Department said. The deputy was in his patrol cruiser near the sheriff’s station in Palmdale, Calif., about a 60-mile drive north of the city of Los Angeles.

Deputy Clinkunbroomer, who had been on duty and in uniform, was shot leaving the Palmdale station while at a red light, officials said. He was rushed to a hospital, where he was pronounced dead from his injuries.

At a news conference on Sunday, Los Angeles County Sheriff Robert Luna said that it was unclear whether there was more than one suspect, and that the authorities did not know of a motive. But officials described a “vehicle of interest” as a 2006-2012 dark gray Toyota Corolla, and they announced a $250,000 award for information leading to a suspect’s arrest and prosecution.

“Please, I beg you. Somebody has information,” he said. “Please make things right.”

Sheriff Luna had said earlier that the shooting was being investigated by “homicide teams, major crimes teams, gang teams.” Investigators believed that the killing was captured on surveillance video, he said, and they were analyzing a video that had been circulating online to determine whether it was related to the shooting.

Deputy Clinkunbroomer, who was transferred to the Palmdale station in July 2018, had worked in the sheriff’s department for about eight years, following in the footsteps of his grandfather and father, Sheriff Luna said. For the past year and a half, he also trained and supervised deputies. “Not just anybody becomes a field training officer,” Sheriff Luna said. “It’s usually the best of the best.”

“Our deputy was a devoted family member and a cherished community member,” Sheriff Luna said in a statement.

Deputy Clinkunbroomer had gotten engaged just four days earlier, he added.

News of the killing rattled officials and residents in Palmdale, a hot, dry city of about 160,000 in far northeastern Los Angeles County. Laura Bettencourt, the city’s mayor, called Deputy Clinkunbroomer a “hero” in a news conference on Saturday night and vowed that the person who shot him, whom she called a “coward,” would be caught.

In a statement posted on X, the platform formerly known as Twitter, Palmdale Sheriff’s Station said that Deputy Clinkunbroomer “strived for excellence in everything he did,” adding that he “genuinely cared for the community he served.”

On Sunday afternoon in Palmdale, many people stopped by the sheriff’s station to pay their respects. A memorial with flowers and candles sprung up on the sidewalk outside the station at Avenue Q and Sierra Highway, the intersection where Deputy Clinkunbroomer was shot.

The site of the shooting and the sheriff’s station sit near a few low-slung homes, some with fences in need of repair. Yellow vans advertising bail bonds are parked, along with other vehicles, in one yard.

Michael Berbiar, 53, a retired Los Angeles County sheriff’s deputy, came to pay tribute with his wife, Yesenia, from their home in Santa Clarita, about 40 miles away.

“I’ve lost several friends and co-workers that have been killed in the line of duty, and this just kind of brings me back to them and how important law enforcement is to the community,” Mr. Berbiar said.

Flowers were also placed by residents on the hood of a police cruiser blocking Avenue Q.

According to statistics released by the F.B.I. on officers killed in the line of duty, there have been five officers who died this year through August in situations designated as “ambushes.” Last year, 12 officers were killed on the job in such situations; eight were killed in 2021 and nine in 2020.

Palmdale has a recent history of tension between law enforcement and the community. In 2015, the U.S. Justice Department and the Los Angeles County Sheriff’s Department announced a settlement involving a set of police reforms in Palmdale and the nearby city of Lancaster after an investigation found patterns of excessive use of force, biased policing practices and unlawful searches and seizures.

Monitors overseeing the reforms in Palmdale and Lancaster have documented a lack of progress in the past two years toward the goals set in the settlement, including a resistance to change and denial of responsibility. Their report this year cited several areas in need of improvement, including daily interactions with the public, but it also recognized “new signs of commitment to reforms” and better communication and transparency.

Tiffany May contributed reporting.