FOOTAGE has emerged of a veteran clashing with a protester shouting "mace me mother f****r" just before he was shot dead in Denver.
Matthew Dolloff, 30, as violence erupted between rival groups in the city on Saturday.
The moments leading up to the deadly shooting were captured in a video which has now been posted on social media,
It shows pro-cop Keltner engaged in a shouting match with ANOTHER man wearing a Black Guns Matter T-shirt.
"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!"
The pair are seen shoving each other with the man then warning Keltner "don't touch...don't touch me."
The counter-protester continues shouting as Keltner walks out of the video frame.
Seconds later a gunshot rings out and Keltner is then seen lying motionless on the pavement.
Keltner was reportedly shot after macing a security guard for the 9NEWS TV crew during Saturday's clashes.
Dolloff was hired by the station to protect their staff at the protest, a practice they said they've been doing "for a number of months".
However, the Denver Department of Excise and Licenses have confirmed there was "no record for an active licensed security guard now or ever" for Dolloff, reported.
"If he was operating as a security guard, he was in violation of the law," department spokesman Eric Escudero told the news station.
"Security guards are prohibited from carrying or using a firearm without getting an armed firearm endorsement for their license.
"All security guards in Denver are required to get a federal background check before they receive their license."
Dolloff was last night being held without bail on suspicion of first-degree murder following the shooting that left Keltner dead.
Keltner had participated in a "Patriot Muster" rally in front of the Art Museum before he was fatally shot.
It's been reported the military veteran
Reports claimed he at an a "- Soup Drive" taking place during the same time as the "Patriot Muster" rally before he was killed.
After the Denver Police Department pinned Dolloff as the suspect, several messages on a Facebook page with his full name and a photo that appears to match his booking photo quickly filled up with hateful messages.
Some users speculated about him having a possible connection to radical left-wing groups.
He appears to be a supporter who attended Occupy protests back in 2012.
But police have sought to dispel rumors about Dolloff having any connections to Antifa.
The Denver Police Department said on Saturday that an investigation determined he had "no affiliation" with the leftist political movement.
However, after the tragedy an Antifa supporter shouting “right in the f***ing dome”.
Older posts on Dolloff's possible Facebook page features photos and articles criticizing .
Most of his social media postings have to do with farm goods he apparently sold in the Denver area, and he appears to be pictured with dogs and sheep.
In the latest public on Dolloff's alleged page, he shared a message mourning the death of progressive political commentator Michael Brooks, who died in July.
"The grief is real, no one better checked my world view more, and his impressions were amazing," he wrote.
"I cant seem to whip away the tears today Michael Brooks was to young [sic] and just getting started #leftisbest #MichaelBrooks I'm going to miss right-wing Mandela ... this is hard to accept."
The dead man sister, Suzan Keltner, on Sunday said her nephew has been struggling to cope after witnessing his father's death.
"He was my brother, my only sibling," Suzan told the . "He also served our country."
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Jay Keltner, who identified himself as one of Lee's sons, also posted about the tragedy on Facebook, writing: "I can't believe my dad's gone. This will never be right #RIP."
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He told the his father wasn't a member of any group and was there "to rally for the police department" as he had done so at previous protests.
It is unclear if Jay was present during his father's death.