A PRO-cop protester was allegedly shot dead by a TV crew security guard after macing him during clashes between Antifa and right-wing militia.
Horrific images show the moment Lee Keltner, believed to be part of a right-wing "Patriot Muster" rally, was fatally shot on Saturday outside the Art Museum in .
The protester maced the security guard, who then pulled out his handgun and shot him dead in the museum's courtyard, the reported.
Keltner was reportedly shot at point-blank range and was taken to the hospital, where he died an hour later, Police Investigations Division Chief Joe Montoya said.
The Denver Police Department identified Matthew Dolloff as the suspected shooter, and disclosed on Sunday afternoon that he is being "held for investigation of first degree murder."
The department noted that the investigation is active and ongoing.
Detectives determined that a "verbal altercation" happened near the museum just before the shooting, Montoya said.
Video shows a man confronting a group of what appears to be protesters, when a man in a baseball hat steps in between them and puts his arms out to separate them, the man says: "Don't f***ing touch me. Touch me one more time; you're gonna get it."
Then speaking to another man, he says: "F***king mace me. Walk up to me and f***ing mace me. Mace me motherf***er."
The man in the baseball cap steps in between them once again as the man continues to yell but is told "don't f***ing touch me, man."
As the man continues to yell at the group what sounds like a gunshot is heard.
DPD confirmed that the security guard wasn't affiliated with the counter-protesting - group.
It was later reported by that he was a contractor the news station hired through Pinkerton.
"A 9NEWS employee and a 9NEWS contractor were taken into custody," the station said, noting that the second of the two people wasn't connected to the shooting.
The producer has since been released from police custody, but the 9NEWS contractor is the suspect detained by DPD.
For several months, 9NEWS has hired private security guards to accompany staff at protests, the news station said.
Video shared on by prominent pro- conservative Ian Miles Cheong claims to show the verbal altercation that led up to the shooting.
A man wearing a "Black Guns Matter" shirt urges a tattooed man wearing a camouflage bucket hat to mace him.
"Mace me, f**kin' mace me brother!" the man yells. "Walk up to me and f***ing mace me n****, mace me mother f****r!"
A woman can be heard in the background asking the man why he's using a racial slur as he continues to shout at the counter-protester.
The bucket hat man clutches what appears to be a can of mace as the two continue to exchange obscenities.
"F**k around and find out!" the man with the Black Guns Matter shirt screams before turning his attention to another man holding a baton.
Moments later, the victim is seen dropping to the floor behind the arguing men after the hiss of an aerosol can and a loud bang.
Two guns were recovered at the scene, and the suspect in custody is being held at police headquarters, DPD said.
A canister of Mace was also recovered at the scene, and detectives are still probing whether it was used in the attack, the police chief said.
Denver Police said later in the evening that the suspect is a private security guard who isn't affiliated with Antifa.
Carol Keltner, who identified herself the victim's mother, shared what happened to her son in a Facebook group called Northeast Arkansas Tea Party Group.
"My son Lee was at the patriot rally today in Denver," .
"After the rally a person on the BLM and Antifa side went up to him said a few nasty words then shot him in the head. He was murdered because he backed the police," she continued.
"His 24 year old son was with him," she added. "I moved to Arkansas because Colorado got too expensive and liberal. The left has gotten out of hand."
Other social media tributes to Keltner have piled up, hailing him as a loving grandfather and a hero veteran, in the hours since the shooting.
Dozens of people gathered in downtown Denver for a "Patriot Muster" rally for a far-right militia group and a "BLM-Antifa Soup Drive" hosted by Denver Communists, Denver-Boulder Socialist Revolution and other groups, according to the event .
The security guard still had his handgun in his clutches, and as cops swarmed him with their guns pointed, he dropped to his knees, raised his hands above his head and released his weapon.
He was arrested at the scene along with the second person who was later believed to have no connection to the shooting.
Local businesses were warned of the potential for escalating violence early Saturday and were told to report seeing protesters wearing helmets, shields, or gas masks ahead of the rallies, KMGH reported.
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Several people were seen fist fighting, and one supporter reported being cracked on the head with a skateboard.
The clash came nearly two months after the death of , which prompted violent clashes between protesters and police across the .