One of three officers wounded in Sunday's shootings was hit in the head and stomach and was fighting for his life, police officials said at a news conference in Baton Rouge, scene of repeated protests against police violence after the July 5 shooting death by officers of Alton Sterling, a black man, outside a convenience store.
"There is no doubt whatsoever that these officers were intentionally targeted and assassinated," Louisiana State Police Superintendent Colonel Mike Edmonson said at the news conference.
"It was a calculated act against those who work to protect this community every single day."
Edmonson said video of the scene showed that the gunman, identified as Gavin Long, "completely dismissed" a number of civilians while walking around with a gun, suggesting that he was deliberately targeting police officers for attack.
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"The most compelling piece of evidence is the video. It is chilling in the sheer brutality of the shooting," Edmonson told reporters.
Authorities said three guns were recovered from the scene, a IWI Tavor SAR 5.56 caliber rifle, a Springfield XD 9.9 mm caliber pistol and a Stag Arms M4 variant 5.56 caliber rifle.
Much was left to be learned about the attack, including the gunman's social media footprint. Edmonson said the gunman "had been in our community for several days" and that while Long was the only gunman on the scene, police could not yet rule out his having assistance in planning the attack.
Police said Long was a 29-year-old from Kansas City, Missouri, who served in the Marines for five years, including a 2008 deployment in the Iraq war.
Long, dressed in black and armed with a rifle, was shot dead on Sunday morning in a gunfight with police.
Racial tension in the United States has been especially high since a black former US Army Reserve soldier fatally shot five Dallas police officers who were patrolling a protest over the police shootings of Sterling and another black man in Minnesota.
Attempted name change
The suspect said he wanted to change his name from Gavin Eugene Long to Cosmo Ausar Setepenra in May 2015, according to Jackson County, Missouri, public records.
But court officials said he never completed the process of legally changing his name.
A website, social media accounts and YouTube videos that appeared tied to Long included complaints about police treatment of black people and praise for killings of the Dallas policemen.
Police said they had not ruled out but had found no evidence to confirm a link with the Sterling shooting.
"Clearly the landscape has changed since Dallas," Edmonson told reporters.
Police said a member of the SWAT team that responded to the scene killed Long with a shot from 100 yards away. East Baton Rouge Parish Sheriff Sid Gautreaux said he had "no doubt" that Long would have killed additional officers if not for that shot.
In a reference to criticism from activists and law enforcement observers that police in the United States had become over-militarised, Baton Rouge Police Chief Carl Dabadie said, "Our militarised tactics, as they're being called, saved lives."
Long also affiliated himself with the Washitaw Nation, an African-American offshoot of the Sovereign Citizen Movement, a group whose members view the federal government as illegitimate.
The dead officers in Baton Rouge were identified as Montrell Jackson, 32; Matthew Gerald, 41; and Brad Garafola, 45.
Two other officers were treated for their wounds in hospital and released.
Memorial at shooting scene
At the B Quick gas station where the shootings occurred, people left flowers and balloons in memory of the slain officers.
"I just want us to have peace and drive down the road and not feel like we have to duck our heads and look around and see if someone's going to be on top of a roof," said Pam Collins, a resident of the Baton Rouge suburb of Prairieville who brought three shiny balloons to honor the officers.
Presumptive Democratic presidential nominee Hillary Clinton, in a speech to the NAACP civil rights group in Cincinnati, said she would bring the "full weight of the law to bear" against cop killers but added that here is "another hard truth at the heart of this complex matter: Many African-Americans fear the police."
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Clinton also said that the police shootings of Sterling in Baton Rouge and Philando Castile in Minnesota "drove home how urgently we need to make reforms to policing and criminal justice (and) how we cannot rest until we root out implicit bias and stop the killings of African-Americans."
Her Republican rival for the presidency, Donald Trump, tweeted that "our country is a divided crime scene" and called for stronger leadership on law and order issues.
US Attorney General Loretta Lynch said agents from the Federal Bureau of Investigation, the Bureau of Alcohol, Tobacco, Firearms and Explosives and the US Marshals Service were in Baton Rouge.
"At the Department of Justice, we are determined to do everything we can to bridge divides, to heal rifts, to restore trust, and to ensure that every American feels respected, supported, and safe," Lynch said in remarks prepared for a conference of black law enforcement officers in Washington.
Louisiana's capital has a long history of distrust between black residents and law enforcement and it has been inflamed by Sterling's death.
For many in Baton Rouge, the police have been viewed as overly aggressive and unrepresentative of a city where more than half the 230,000 residents are black.
The violence has heightened security concerns, notably for the Republican convention beginning in Cleveland on Monday ahead of the Nov. 8 presidential election, and the Democratic convention in Philadelphia.
