The man shot dead at a Denver protest was a military veteran, grandfather and avowed patriot who was there to express his support for police and died as his son looked on in horror, according to his mom. 

Lee Keltner was identified by his mother, Carol, in a Facebook post to the group Northeast Arkansas Tea Party Group. The heartbroken mom said her grandson was with his father when he was killed by a man working as a security guard for a local TV station.

“My son Lee was at the patriot rally today in Denver,” she wrote to the group. “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.”

“His 24-year-old son was with him. I moved to Arkansas because Colorado got too expensive and liberal,” she added. “The left has gotten out of hand.”

According to a profile in the Denver Post, Keltner was a hatter at Crossfire Hatters, having worked for over 25 years.

DENVER, COLORADO - OCTOBER 10: A man punches another man after a rall in Denver, Colorado, on October 10, 2020. The man on the left side of the photo was supporting the "Patriot Rally". He engaged with the man on the right, hit him in the face and sprayed him with mace. The man at right, then shot and killed the protester. (Photo by Helen H. Richardson/MediaNews Group/The Denver Post via Getty Images) (Getty)

Keltner was taking part in a pro-police “Patriot Rally” near the Denver Art Museum when he was allegedly shot dead by Matthew Dolloff, a private security guard hired by KUSA-TV – a local Denver news station also known as 9NEWS.

"There was a verbal altercation that transpired. A firearm was discharged," Joe Montoya, Denver Police chief of investigations, said. "An individual was shot and later pronounced deceased. There were two guns recovered at the scene."

Matthew Dolloff Courtesy Denver Police/ Twitter

Dolloff was taken into custody by the Denver Police Department on suspicion of first-degree murder, though he has not been formally charged.

Dolloff was contracted through Pinkerton by 9NEWS – a practice the station has followed for a number of months during the widespread protests.

Matthew Dolloff / Facebook

Shortly after he was identified, past posts by Dolloff surfaced, showing that he was more overtly left-leaning politically, with posts talking about how a Trump Button was a “racist button” and calling the Trump administration a "fascist dictatorship."

The shooting occurred during dual protests – the “Patriot Muster” pro-police groups and a “Black Lives Matter Anti-Fascist Soup Drive,” the latter of which included Denver Communists, Colorado Socialist Revolution, Anon Resistance Movement, W.I.T.C.H. Denver, H.O.E.S (Help on Every Street) and Front Range Mutual Aid Network.

"There was a large presence because we had two groups with opposing views, and we know that can always get very tense," Montoya said. "There’s always potential for violence, we understand that.”

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“We had a large contingent there to try to watch the egress of one group, so that the other group wouldn’t intermingle with them, so that’s the reason for the large presence there."

Fox News' Paul Best contributed to this report.