Records show that he served in the Marine Corps as a data network specialist for five years, was deployed to Iraq in 2008 and received a handful of medals for his service. Officials are probing what links he may have had to an anti-government group for which he had shown support, a source familiar with the investigation said.

Earlier in the day, there appeared to be some doubt whether Long acted alone or had accomplices.

The Associated Press reported that two people of interest had been detained. Late on Sunday the Louisiana State Police said two people were released without charges.

"We believe the person that shot and killed our officers, that he is a person that was shot and killed at the scene," Louisiana State Police Superintendent Col. Mike Edmonson had said earlier.

The Sunday morning attack came in the wake of the death of Alton Sterling, a black man who was shot and killed during an altercation with Baton Rouge police officers on July 5.

Protesters took to the streets nationwide after video surfaced of his fatal encounter, which was followed the next day by a video of the fatal police shooting of a black man in Minnesota. Sunday`s attack comes as the country also reels from the killing of five officers in Dallas on July 7 by a gunman who said he was angry at police.

Violent speech has surfaced online in the controversy surrounding the recent shootings. In a warning, the FBI cited calls on social media to "purge" cops in Baton Rouge.

A notice put out by the FBI`s New Orleans field office on July 7 mentioned "threats to law enforcement and potential threats to the safety of the general public" stemming from Sterling`s shooting.

The FBI said the information was not officially confirmed but was issued to alert law enforcement to be aware.

The Louisiana State Police Department is leading the investigation into the most recent shooting.

The FBI New Orleans office said it "has personnel on scene in Baton Rouge to assist our law enforcement colleagues ... At this time, our focus is to help identify and bring to justice those who are responsible for this heinous act."

The Department of Homeland Security said it is "in contact with the FBI, Baton Rouge law enforcement and our fusion center partners there, and ... Secretary [Jeh Johnson] has directed that the full weight of the department`s resources be made available."

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