The single gunshot that killed Long, 29, was fired by an officer from about a hundred yards away, police officials said on Monday
The three lawmen shot dead in Baton Rouge, Louisiana, were deliberately "targeted and assassinated" by a U.S. Marine Corps veteran who appeared to go out of his way to spare the civilians he encountered during his assault, police officials said.
Former Sergeant Gavin Eugene Long, an Iraq war veteran with ties to an African-American anti-government group, seemed determined to slay as many police officers as possible before a SWAT team marksman cut short his attack on Sunday, according to authorities' account the next day.
The single gunshot that killed Long, 29, was fired by an officer from about a hundred yards away, police officials said on Monday as they deepened their investigation into the second racially charged armed assault on U.S. law enforcement this month.
The ambush came a week and a half after another former U.S. serviceman espousing militant black nationalist views cut down five Dallas officers in a sniper attack that shattered an otherwise peaceful protest denouncing the fatal police shootings of two black men days earlier, one of them in Baton Rouge.
Police have declined to say what role race might have played in Sunday's shooting rampage, which left two white officers and one black officer dead, and three more lawmen wounded, one of them critically.
But Long, who was black, said in a series of social media messages posted in recent days, some from Dallas, that he was fed up with the mistreatment of African-Americans at the hands of law enforcement, and praised the attack on Dallas police.
Legal papers filed in his home state of Missouri showed he was affiliated with Washitaw Nation, a black offshoot of the Sovereign Citizen movement, which challenges the legitimacy of the federal government.
As evidence of Long's single-minded intent to level his violent rage exclusively at police, authorities on Monday cited video footage of the shooting that they said showed him hunting down officers while bypassing civilians in his path.
"There is no doubt whatsoever that these officers were intentionally targeted and assassinated," Louisiana State Police Superintendent Colonel Mike Edmonson told a news conference. "It was a calculated act against those who work to protect this community every single day."
Police said they believed that Long, armed with two rifles and a pistol, had intended to make his way to the headquarters of the Baton Rouge Police Department a short distance away to take more lives.
The carnage rocked a city still shaken from days of angry protests and tension over the fatal police shooting on July 5 of a 37-year-old black man, Alton Sterling, who was confronted by officers while selling CDs outside a Baton Rouge convenience store. Sterling was buried just last Friday.
A day after his killing, another black man, Philando Castile, 32, was shot to death by a policeman during a traffic stop near St. Paul, Minnesota.
The back-to-back killings reignited nationwide protests over the use of force by police against minorities, including the fateful rally in Dallas on July 7.
Edmonson said Long, a resident of Kansas City, Missouri, had been in the Baton Rouge area for several days before the shooting and, while he acted alone in the ambush itself, police had not ruled out the possibility that he might have had help in planning the attack.
Military records released by the Pentagon showed Long, listed as a data network specialist, served five years in the Marine Corps until his discharge in August 2010, including a six-month deployment to Iraq.
The dead officers in Baton Rouge were identified as Matthew Gerald, 41, also an Iraq war veteran and father of two; Montrell Jackson, 32, who was black and had served as a Baton Rouge police officer for a decade; and sheriff's deputy Brad Garafola, 45, a father of four.
President Barack Obama offered his condolences in telephone calls on Monday to the victims' loved ones as well as top law enforcement officials in the city.
Hundreds of mourners held a candlelight vigil on Monday evening at a church in south Baton Rouge in memory of Gerald, a rookie on the police force who had served in both the U.S. Army and the Marines.