Separate weekend shootings in the U.S. have left one police officer dead and another in critical condition in what authorities are calling targeted attacks.
The two incidents, in Texas and Missouri, were part of a weekend of violence also involving police shootings in Florida and Missouri.
In the Texas case, a San Antonio detective writing out a traffic ticket to a motorist was shot dead in his squad car late Sunday morning outside police headquarters by another driver who pulled up from behind, authorities said.
San Antonio police Chief William McManus identified the officer as Benjamin Marconi, 50, a 20-year veteran.
McManus said at a news conference Monday morning that he thinks "the uniform was the target." 
Benjamin Marconi
Marconi, 50, was shot to death in his squad car while writing out a traffic ticket. (San Antonio Police Department via AP)
"Anyone [in a police uniform] who happened along was the target," he said. 
Police are asking the public for help in identifying the suspect — who appeared at the San Antonio police headquarters about four hours before the shooting. Surveillance video shows a black man likely in his 20s who was dressed all in black.
McManus said earlier he didn't believe the suspect has any relationship to the original motorist who was pulled over, and no motive has been identified.
In St. Louis, a 46-year-old police sergeant was in critical condition in hospital but expected to survive after he was shot in the face Sunday night in what the police chief called an "ambush." Police said early Monday that the suspect was later killed in a shootout with police.
Police Chief Sam Dotson said the sergeant was shot twice in the face.
"Fortunately for the blessing of God the officer's going to survive," Dotson said during a brief news conference after the shooting. He declined to name the sergeant but said he is a married father of three who has been with the department for about 20 years.

Suspect killed in St. Louis

The police sergeant was not involved in a call or a traffic stop but was sitting in traffic about 7:30 p.m. Sunday when another car pulled up alongside his marked police vehicle. The sergeant told police he heard at least two shots.
"This officer was driving down the road and was ambushed by an individual who pointed a gun at him from inside of his car and shot out the police officer's window," Dotson said.
Police reported that officers later pulled up behind the suspect's vehicle and that he fled on foot. Police said the man fired shots at the officers, who returned fire, killing him. No officers were shot.
Two other police officers in other states were also shot Sunday night, but it wasn't clear whether the incidents were targeted attacks. 
An officer with the Gladstone, Mo., police department near Kansas City was shot, along with a suspect. Meanwhile, an officer in Sanibel, Fla., was shot in the shoulder during a traffic stop, and was treated and released. The suspect was arrested, according to local media. 
Officer Killed San Antonio
An American flag and a Texas state flag fly at half-mast at San Antonio Police Department headquarters near a sign and flowers. (Edward A. Ornelas/The San Antonio Express-News/Associated Press)

'Horrific act'

Sunday's fatal shooting in San Antonio came less than five months after a gunman killed five officers in Dallas who were working a protest about the fatal police shootings of black men in Minnesota and Louisiana. 
Ten days after the Dallas attack, a man wearing a ski mask and armed with two rifles and a pistol killed three officers in Baton Rouge, La. Earlier this month, two Des Moines, Iowa-area police officers were fatally shot in separate ambush-style attacks while sitting in their patrol cars.
"It's always difficult, especially in this this day and age, where police are being targeted across the country," McManus said.
Texas Gov. Greg Abbott called the slaying of Marconi a "horrific act of violence." Abbott said in a statement that "attacks against law enforcement officers will not be tolerated in Texas and must be met with swift justice."
St Louis Officer Shot
Police investigate a scene after a St. Louis police officer was shot in what the police chief called an 'ambush' on Sunday night. (David Carson/St. Louis Post-Dispatch via AP)
With files from Reuters and CBC News
© The Associated Press, 2016
The Canadian Press