Gunman Identified in Shooting That Killed 3 Baton Rouge Officers "This is truly a sad day in Baton Rouge," Mayor Kip Holden said.

 -- Three law enforcement officers in Baton Rouge, Louisiana, were killed on Sunday, and three others were wounded in an apparent attack by a former U.S. Marine.

Officers Montrell Jackson, 32, and Matthew Gerald, 41, of the Baton Rouge Police Department and Brad Garafola, 45, of the East Baton Rouge Sheriff’s Department lost their lives.

The gunman was identified as Gavin Long, 29, who officials said died at the scene. Long had driven to Louisiana from his home in Kansas City, Missouri, and opened fire on the officers as they responded to a 911 call, officials said.

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."

Last week Alton Sterling's 15-year-old son, Cameron Sterling, urged Baton Rouge residents to "protest in peace."

The Baton Rouge officers who died on Sunday were responding to a 911 call around 8:45 a.m. about a man dressed all in black walking around with a rifle in the Old Hammond area — less than a mile from police headquarters — officials said.

"This is truly a sad day in Baton Rouge," Mayor Kip Holden said. "We continue to ask the question and continue to make the statement, 'Let peace prevail in Baton Rouge and this parish.' We must look ahead. We thank our officers who have fallen in the line of duty, we pray for their families, and we pray for peace everywhere."

Louisiana Gov. John Bel Edwards said in a statement, "This is an unspeakable and unjustified attack on all of us at a time when we need unity and healing. Rest assured, every resource available to the state of Louisiana will be used to ensure the perpetrators are brought swiftly to justice."

President Barack Obama told reporters, "This has happened far too often."

"I know whenever this happens, wherever this happens, you feel it. Your families feel it. But what I want you to know today is the respect and the gratitude of the American people for everything that you do for us," he said.

Obama mentioned how he traveled to Dallas five days ago for a memorial service for the five officers killed there. "I said that that killer would not be the last person who tries to make us turn on each other, nor will today's killer," he said.

He said in a statement earlier today, "I condemn, in the strongest sense of the word, the attack on law enforcement in Baton Rouge. For the second time in two weeks, police officers who put their lives on the line for ours every day were doing their job when they were killed in a cowardly and reprehensible assault. These are attacks on public servants, on the rule of law and on civilized society, and they have to stop."

He said he has offered the support of the federal government to state and local authorities in Louisiana.

"And make no mistake — justice will be done," he said. "We may not yet know the motives for this attack, but I want to be clear: There is no justification for violence against law enforcement. None. These attacks are the work of cowards who speak for no one. They right no wrongs. They advance no causes. The officers in Baton Rouge, the officers in Dallas — they were our fellow Americans, part of our community, part of our country, with people who loved and needed them and who need us now, all of us, to be at our best."