Investigators trying to figure out why a former Marine sergeant would eventually kill police in broad daylight will likely look to the writings and online footprint of Cosmo Setepenra, the name Long legally changed his name to.
Setepenra wrote books about "esoteric health and nutritional practices" and "how to develop your higher-self."
On two websites he describes himself as a "Freedom Strategist, Mental Game Coach, Nutritionist, Author and Spiritual Advisor."
And in one video online he claims that victims of bullying need to resort to brute force: "100% have been successful through fighting back. Through bloodshed. Zero have been successful just over simply protesting. It has never worked, and it never will."
Here's what we know about Long's background and the views and opinions he espoused under the Setepenra pseudonym.
Long's time in Dallas
In a video posted on YouTube July 10, Long, who was African-American, speaks at the camera eloquently about recent protests and officer-involved shootings, often employing the motifs of blood and money and revolution.
He cites figures ranging from Nat Turner to Malcolm X and George Washington.
That video, he says, was recorded from Dallas, where five police officers were recently killed by a sniper targeting cops.
Long mentions the July Fourth holiday as a celebration of an uprising against oppressive forces, and without mentioning Micah Xavier Johnson -- the Dallas shooter -- by name, he questions why some violent actions are perceived as criminal while others are celebrated.
A video posted two days earlier is a bit more cryptic, but makes more sense in the aftermath of his shooting rampage.
"I just wanted to let y'all know, don't affiliate me with nothing," he says. He says he wanted people to know that his actions were his alone.
He then goes on to list organizations that he says he has no affiliation with -- including the Nation of Islam, Floyd Mayweather's The Money Team (he's wearing their hat) and terror groups like ISIS.
"I thought my own stuff; I made my own decisions; I'm the one who gotta listen to the judgment," Long added.
Those who knew him
Carl Woodley, Long's stepfather, said he was in "total shock" about the Baton Rouge shootings. He said he was sorry about what happened to the officers and about losing his stepson.
Woodley said Long was about 7 when they met and he remembered Long as a good, quiet and intelligent boy.
"I never had ... problems with him," he added. "He wasn't my biological son, but he was a son to me. ... We were real close."
As an adult, Long, who was once overweight, often offered his stepfather nutritional advice.
Woodley said he last spoke to Long in May, when his stepson gave him a book on nutrition, ordered vitamins for him online and recommended a cleanse.
Long never talked to him about anger toward the police or the way they treated blacks, said Woodley, who added that he did not follow his stepson on social media. Woodley said he never saw Long with a weapon.
Woodley was with Long when the young man enrolled in the U.S. Marines in 2005. When Long was discharged in 2010, the military veteran was "more like a loner, stayed to himself," Woodley said.
Long's stepsister, Brittany Woodley, on Facebook recalled fond memories of times when he babysat her.
"He never was mean," she told CNN, adding that her recent contact with Long came on Facebook.
"He was always kind, always humble. He was outspoken. Just a very good person."
Cousin Kendall Fryer said via Facebook that Long "is nothing like he is portrayed to be" since the shootings, but declined further comment out of respect for the family.
"Lord knows we wanna say something," Fryer said.
The Washitaw Nation
After he was killed, investigators found a card on Long's body suggesting he was a member of the Washitaw Nation, according to two law enforcement officials.
The Southern Poverty Law Center describes the Washitaw Nation "as a sovereign tribe descended from pre-Columbian blacks who settled in North America."
Long legally changed his name to Cosmo Ausar Setepenra in May 2015, claiming that he was "seeking to correct" his name, because he was part of the indigenous society, United Washitaw De Dugdahmoundvah Mu'er nation.
The group is one of many fringe groups to which the gunman may have belonged.
Long followed several conspiracy groups devoted to government surveillance and monitoring. An email address linked to him showed that he was a member of a support group in an organization called Freedom from Covert Harassment and Surveillance.
The group's mission is to help those "marginalized and abused by ... remote brain experimentation, remote neural monitoring of an entire human's body."
On that site he's identified as a "Buddy" representing other "targets" of government surveillance.
The FBI is vetting the claim Long made on YouTube that he was a member of the Nation of Islam. An official said the belief is that Long identified as being associated with the black separatist movement in some capacity but there is no indication he was directed by it. The law enforcement official said the FBI has no indication any black separatist or other domestic terrorist groups are supporting or sending people to kill police officers.
Long joined the Marines in 2005 and worked as a data network specialist, according to the U.S. military.
He was deployed to Iraq and spent time in California and Japan before being discharged at the rank of sergeant in 2010.
He received a handful of awards, including the Marine Corps Good Conduct Medal.
Two law enforcement sources told CNN that Long rented a car in Kansas City after the Dallas shootings and drove it to Baton Rouge.
Since one of his YouTube videos was posted from Dallas on July 10, it's likely he made the trip to Baton Rouge from Dallas.
He was not alone during his stay in Baton Rouge, a law enforcement source told CNN. But, it's unclear if his associates were actively involved in any plot.
The shooting began Sunday when police received a call of a "suspicious person walking down Airline Highway with an assault rifle," a source with knowledge of the investigation told CNN.
When police arrived, they were ambushed. Long was wielding an AR-15 style semi-automatic rifle, law enforcement sources told CNN.
"There was no talking, just shooting," Baton Rouge police Cpl. L.J. McKneely said.
Police officers who responded to Sunday's shootings killed Long in a minutes-long gunbattle.
"He wasn't robbing a bank," an official told CNN. "He was armed to shoot it out with police."
Correction: An earlier version of this article incorrectly described Long's comments about the Nation of Islam and Floyd Mayweather's The Money Team. Long said he had no affiliation with the groups. Mayweather's representative said he has no association with anyone who would advocate harm to law enforcement officers.