Houston — Houston authorities said they have arrested a 31-year-old man in the ambush slaying of a veteran sheriff's deputy.  

Harris County Sheriff Ron Hickman identified the suspect as Shannon J. Miles. He described the killing as a “senseless and cowardly act” and called Miles a “significant threat to law enforcement and community at large.”

Miles is in custody on a charge of capital murder.

Hickman said Miles has a criminal record, including resisting arrest and disorderly conduct with a firearm. Hickman, speaking at an afternoon news conference, said it appeared Deputy Darren Goforth was targeted because he was a law enforcement officer but added that the exact motive for the shooting is not yet known.

Earlier on Saturday authorities had called on the public to help catch the gunman. While emphasizing they did not know the motive for the killing, officials decried the recent stridency of anti-police rhetoric.

Harris County District Attorney Devon Anderson, without offering specifics, appeared to allude to recent shootings and incidents involving police officers that have been widely condemned.

“Please come forward if you have any information,” Anderson said. “It is time for the silent majority in this country to support law enforcement. There are a few bad apples in any profession. That does not mean there should be open warfare declared on law enforcement.

“The vast majority of officers are there to do the right thing — are there because they care about their community and want to make it a safer place. What happened last night was an assault on the very fabric of society, and it is not anything we can tolerate.”

Goforth, 47, a 10-year veteran of the force, was in full uniform, filling up his patrol car at a Chevron station northwest of Houston, when a man approached him from behind Friday night and shot him multiple times, sheriff’s officials said. He died at the scene.

A witness called 911, and investigators responded from the Harris County Sheriff’s Office, Texas Department of Public Safety and Harris County Constables.

Anderson was joined at a news conference Saturday morning by Hickman, who noted the “dangerous national rhetoric that is out there today,” presumably referring to anger directed at law enforcement. “This rhetoric has gotten out of control,” he said.

Many have been tweeting Saturday about a possible connection between the deputy’s shooting and calls for attacks on law enforcement earlier this week on a Houston-area radio show. The hashtag FYF911 appearing on many of the tweets is being used by a group organizing a protest on Sept. 11 in Atlanta where they say will burn U.S. and Confederate flags and police uniforms.

Hickman said investigators were aware of the comments, adding they were not questioning anyone from those groups but “we always follow that rhetoric” and “we won’t leave any stone unturned.”

“Until we know with absolute certainty what the motive is, it’s all speculation,” he said.

He added that the killing “strikes at who we are as police officers.”

Hickman did not specifically mention deaths of citizens at the hand of law enforcement officers that have sparked controversy in the past year, such as the police shooting of Michael Brown in Ferguson, Mo., but did note that this incident did not involve a confrontation with an officer. It was a “cold-blooded execution,” he said.

Hickman said Goforth was alone at the time of the shooting.

Early Saturday, investigators were reviewing surveillance video from the gas station, still searching for the shooter and a motive. Video showed a man wearing a white T-shirt and red shorts and traveling in a maroon or red Ford Ranger.

Texas Gov. Greg Abbott tweeted, “Prayers Please for family of this Texas sheriff’s deputy who was shot & killed Friday near Houston.”

A sheriff’s office spokesman tweeted, “We lost one of our brothers tonight” and “Our hearts are broken.”

A spokesman for the 100 Club, which supports law enforcement, said at the briefing that the group was preparing to give $20,000 to support the deputy’s family, including his two children, ages 12 and 5.

According to the National Law Enforcement Officers Memorial Fund, a nonprofit group that maintains a database of officer deaths, 80 law enforcement officers have been killed in the line of duty since Jan. 1 of this year, compared with 73 during the same period in 2014. Of the 80 officers, 24 were killed by gunfire.

A report by the organization says that firearms-related fatalities peaked in 1973, with 84 officers shot and killed in the first six months of that year, and have since decreased from 62 on average in the 1970s, to 29 on average in the 2000s.

Late last year, two New York City police officers, Wenjian Liu and Rafael Ramos, were killed in an ambush attack while sitting in their patrol car in the Bedford-Stuyvesant neighborhood of Brooklyn. The shooting, which was carried out by a lone gunman who later committed suicide, was called a revenge attack for the deaths of Eric Garner and Brown, black men who died in confrontations with police.

On Wednesday, a Louisiana police officer, Henry Nelson, was killed by gunfire after he responded to a domestic violence call. On Sunday in the southwest part of that state, a state trooper, Steven Vincent, was killed when he attempted to arrest a driver suspected of being under the influence. And last week, a deputy sheriff in Nevada, Carl Howell, was shot and killed while responding to domestic violence report in Carson City.

The killing of the deputy outside Houston comes after a June attack on police headquarters in Dallas. In that incident, the suspected shooter fired more than 30 rounds into the building’s lobby before fleeing in an armored van. The suspect, who left pipe bombs near the headquarters, was heavily armed and espoused hatred for Jews, Christians and others. He was later shot and killed by police.

That attack echoed a previous shooting by another lone heavily armed gunman and white supremacist at Austin, Texas, police headquarters last year.

No police were injured in those shootings.

Times staff writers Nigel Duara in Phoenix and Natalie Schachar in Los Angeles contributed to this report.