A gunman who murdered three Louisiana police officers in an ambush "was seeking out police", investigators have confirmed.
State police also officially identified the Baton Rouge gunman as former US Marine Gavin Long, who was killed at the scene.
The shooting on Sunday also left three officers injured, one critically.
Col. Mike Edmonson said Long's "movements, his direction, his attention, was on police officers".
Mr Edmonson also said investigators have interviewed people who had contact with the gunman in Baton Rouge, but officials are still asking any others who might have known him to come forward.
The shooting, less than a mile from police headquarters, added to the tensions across the country between the black community and police.
Long, from Kansas City, Missouri, turned 29 on Sunday, the same day he opened fire.
Just days earlier, one of the murdered officers posted an emotional Facebook message about the challenges of police work in the current environment.
US President Barack Obama urged people to tamp down inflammatory words and actions. "We don't need careless accusations thrown around to score political points or to advance an agenda. We need to temper our words and open our hearts... all of us," he said.
Long, who was black, served in the marines from 2005 to 2010, reaching the rank of sergeant. He deployed to Iraq from June 2008 to January 2009, according to military records.
He had no known ties to any extremist groups.
Although he was believed to be the only person who fired at officers, authorities said they were unsure if he had some kind of help. "We are not ready to say he acted alone," state police spokesman Major Doug Cain said.
Two "persons of interest" were detained for questioning in the nearby town of Addis but were later released without charge.
Mr Cain said authorities planned to continue investigating whether the gunman had any assistance "indirectly, directly here or at home".
While in the military, Long was awarded several medals, including one for good conduct, and received an honourable discharge. His occupational expertise was listed as "data network specialist".
It is the fourth high-profile deadly encounter in the United States involving police over the past two weeks. In all, the violence has cost the lives of eight officers, including those in Baton Rouge, and two civilians and sparked a national debate over race and policing.