BATON ROUGE, La. (CBSNewYork/AP) — Police in Baton Rogue described in detail Monday, how a gunman targeted and killed three officers at close range, and wounded three others.

Louisiana State Police Col. Mike Edmonsdson says the gunman who shot six police officers in Baton Rouge clearly targeted law enforcement, carrying two riles and a 9 mm handgun in Sunday’s ambush.

READ MORE: New York Weather: CBS2's 1/27 Thursday Afternoon Forecast

Edmonson showed overhead maps of the area to explain how black former Marine Gavin Long snuck up behind police officers and shot them at close range.

He says another deputy had spotted the gunman’s car and was about to run his license plate when the gunman shot the deputy — “that’s the one critically injured, fighting for his life right now.”

Edmonson said a responding SWAT team officer finally shot the gunman from about 100 yards away.

Baton Rouge continues to mourn as investigators try to determine what motivated Long to open fire on police, killing three officers and injuring three others.

As CBS2’s Chris Martinez reported, officials released chilling surveillance images of Long dressed in black, armed with an assault rifle, as he carried out his deadly ambush.

“There is no doubt these officers were intentionally targeted and assassinated. It was a calculated act against people who work to protect this community every day,” Edmondson said.

The shooting began when officers responded to a call about an armed man dressed in black. Police said Long was targeting police. He died in a shootout with officers.

Three officers from two different departments were killed.

One was 32-year-old Montell Jackson, a 10-year veteran on the Baton Rouge police force. He was married with a 4-month-old son, Mason.

Also killed was 45-year-old Brad Garafola, who had a 24-year career as a sheriff’s deputy. He was a father to four children.

The third was 41-year-old Matthew Gerald. He was new to the police force, just four months in after serving as a Marine.

Gerald had served as a Marine Corps blackhawk crew member. He served three tours overseas.

Three other officers were taken to the hospital, one in critical condition.

As part of their investigation, authorities are examining the gunmen’s social media activity for clues into the attack.

CBS News has learned Long, whose last known address was Kansas City, was part of a group that believes government and law enforcement do not have any authority.

Louisiana Gov. John Bel Edwards said Long “came in here from somewhere else to do harm to our community.”

“This was a diabolical attack on the very fabric of our society. This is not hyperbole. It is not an overstatement. There is nothing more important than law and order,” Edwards said.

Edwards added that killing police officers “doesn’t accomplish anything, it’s not constructive. It’s just pure unadulterated evil.”

Long posted his thoughts in a series of YouTube videos.

“I thought my own thoughts, I made my own decisions, I’m the one who gotta listen to the judgment,” Long said in one video.

In a video posted 10 days before the shooting, Long said he was “affiliated with the spirit of justice.”

READ MORE: Child Hospitalized After Being Struck By Vehicle In Brooklyn

“Don’t affiliate me with nothing,” Long said. “Yeah, I was also a Nation of Islam member, I’m not affiliated with it. … They’ll try to put you with ISIS or some other terrorist group — no.”

Long also sought to change his name to Cosmo Setepenra in a document filed in May 2015 with the Jackson County Recorder of Deeds.

The name-change document ends: “Standing firm on the Ancient Principles of, LOVE, TRUTH, PEACE, FREEDOM AND JUSTICE.”

According to CBS News, Long was honorably discharged from the Marines in 2010 after serving since 2005.

Long carried out the attack on his 29th birthday.

A day after the shooting there was till a great sense of disbelief in the community. Many were leaving flowers and small crosses near the crime scene.

A police chaplain put up crosses and read scriptures near the convenience store where authorities said  Long, ambushed the officers on Sunday.

“The community is just torn up, too much violence,” said resident Nerissa Vandewalker.

Tensions between police and the communities have been high in Baton Rouge and around the country since the killings of five police officers in Dallas and the recent police-involved killings of Alton Sterling and Philando Castile.

“If we come together as a family, peacefully and talk it out, we can fix our problems,” said Baton Rouge Police Chief Carl Dabadie, Jr.

President Barack Obama is asking the American people to make certain the killer’s work to divide the public would be in vain.

“It remains up to us to make sure that they fail. That decision is all of ours,” he said.

On Monday, presumptive Democratic nominee Hillary Clinton said the recent killings of police officers in Dallas and now in Baton Rouge threaten the ability of the nation to make progress. She says police “represent the rule of law itself. If you take aim at that and them, you take aim at all of us.”

The former secretary of state says anyone who kills a police officer or acts as an accomplice must be held accountable.

After the attack in Baton Rouge, two people were taken into custody who were believed to be connected with the shooting, but they were later released. Police believe Long acted alone.

The attack has put police stations across the country on high alert, including in New York City.

The NYPD released a memo Sunday telling officers to stay alert at all times, especially when approached by the public.

On the CBS Evening News, NYPD Commissioner Bill Bratton said more needs to be done to build trust between minority communities and the police.

“We need to find ways to see each other, to hear each other, to find common ground that we can stand on and have dialogue and not assassinations, not murders, not violence,” he said. 

The memo also says officers will continue to patrol in pairs, as they’ve been doing since the shooting in Dallas.

On Long Island, members of the Nassau County Police Department laid a wreath in front of their headquarters Monday, honoring the officers who died in the shootout, WCBS 880’s Mike Xirinachs reported.

“Now more than ever, it is important that we who are sworn to protect and serve watch out for each other and remain constantly vigilant,” Chief of Department Steve Skrynecki said.

MORE NEWS: Remembering Officer Rivera: Wake Today For 22-Year-Old Killed In Line Of Duty In Harlem

(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)