The weekend shootings of police officers in Texas and Missouri follow a string of attacks on officers around the country, many of them deadly.

In San Antonio, a detective was shot and killed while writing a traffic ticket in his squad car Sunday morning outside police headquarters, authorities said. In St. Louis, a police sergeant was hospitalized in critical condition Sunday evening after he was shot twice while sitting in traffic in a marked police vehicle. In other cases:

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Nov. 2: Two Des Moines, Iowa area police officers were fatally shot in separate ambush-style attacks while they were sitting in their patrol cars. Scott Michael Greene, an unemployed 46-year-old father, is charged with killing first-year Urbandale police officer Justin Martin, 24, and Des Moines Police Sgt. Anthony Beminio, 38, within minutes of each other.

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July 17: A Missouri man armed with two rifles and a pistol and wearing a ski mask ambushed and killed three officers near a gas station and convenience store in Baton Rouge, Louisiana. The gunman, Gavin Long, was killed by police. His mother said the Iraq war veteran suffered from post-traumatic stress disorder.

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July 7: A gunman in Dallas opened fire on police officers working at a protest about recent killings by police of black men in Minnesota and Louisiana. The attacker, Micah Johnson, killed five officers and wounded nine others and two civilians before police killed him with a robot-delivered bomb when negotiations failed. Authorities say Johnson, who was black, told negotiators he wanted to kill as many white police officers as he could. It was the deadliest day for American law enforcement since Sept. 11, 2001.

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Dec 28, 2015: Officer Guarionex Candelario Rivera showed up unannounced at his police station in Ponce, Puerto Rico, and fatally shot three fellow officers. Candelario, a 19-year police veteran, killed Lt. Luz Soto Segarra, Cmdr. Frank Roman Rodriguez and policewoman Rosario Hernandez De Hoyos. Candelario was shot twice but survived.

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July 13, 2014: Jersey City, New Jersey Officer Melvin Santiago was shot in the head by a man who had grabbed a security officer’s gun, waited for police to arrive and then opened fire outside a drug store. The shooter was killed by other officers. Investigators later said the suspect had alcohol and PCP in his system and cocaine in his possession.

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May 9, 2015: Two Hattiesburg, Mississippi, police officers, Benjamin Deen and Liquori Tate, were shot to death during a traffic stop. Three suspects were later arrested.

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Dec 20, 2014: Two New York City police officers, Wenjian Liu and Rafael Ramos, were ambushed and fatally shot while in their vehicle without warning by a man who approached the passenger window of their marked police car. The suspect, 28-year-old Ismaaiyl Brinsley, then fatally shot himself. Brinsley was black; the officers were Asian and Hispanic, police said. The shooting came amid heightened tensions between law enforcement and minority communities.

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September 12, 2014: A survivalist ambushed two Pennsylvania state troopers outside of a police barracks late at night, killing Cpl. Bryon Dickson and wounding Trooper Alex Douglass. Suspect Eric Frein led authorities on a 48-day manhunt through the heavily wooded Pocono Mountains before U.S. marshals captured him at an abandoned airplane hangar. He has pleaded not guilty.

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June 8, 2014: A man and a woman ambushed two police officers eating lunch at a Las Vegas pizza restaurant, fatally shooting them before fleeing to a nearby Wal-Mart where they killed a third person and then themselves in an apparent suicide pact. Officers Alyn Beck and Igor Soldo died.

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May 25, 2013: Bardstown, Kentucky Police Officer Jason Ellis was fatally shot in an ambush as he cleared debris from a parkway exit ramp. Investigators believe tree limbs were put on the exit ramp to force Ellis to stop.

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Aug. 28, 2010: Two police officers were ambushed in a tiny Alaskan village of Hoonah before a SWAT team and dozens of other law officers surrounded a house where the gunman took refuge. Officers Tony Wallace and Matt Tokuoka died after the shooting. Hoonah resident John Marvin Jr. was captured and charged in the deaths.

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May 20, 2010: Two West Memphis, Arkansas, police officers doing anti-drug work were shot to death by two men wielding AK-47s along a busy Arkansas interstate. Sgt. Brandon Paudert and Officer Bill Evans died at a nearby hospital. The suspects were later killed in a shootout that injured the local sheriff and a deputy at a crowded Wal-Mart parking lot.

(AP)