A Louisiana man was arrested over the weekend in a series of shootings that left two people dead, including a state trooper whose death was not discovered for more than 12 hours after he was shot, the authorities said.

Master Trooper Adam Gaubert of the Louisiana State Police was found dead in his police car around 5 p.m. Saturday in Ascension Parish, the State Police said at a news briefing on Monday. They said that Matthew Reese Mire, 31, had ambushed Trooper Gaubert, 47, sometime around 2:30 a.m., after the trooper had parked his car to fill out some paperwork.

“Losing a co-worker like Adam puts a hole in your heart,” Col. Lamar A. Davis, the superintendent of the State Police, said at the briefing. He said that it was “absolutely unacceptable” that it took so long for the police to discover that Trooper Gaubert, a 19-year agency veteran, had been fatally shot.

Colonel Davis said that the delay in discovering the killing had prompted the State Police to consider procedural changes, including “expanded GPS coverage, dormant activity alerts and redundant personnel tracking by supervisors.”