Colorado prosecutors have charged the unlicensed security guard accused of fatally shooting a protester last weekend with murder

Matthew Dolloff, 30, faces a second-degree murder charge in the death of 49-year-old Lee Keltner during dueling left and right-wing rallies on Oct. 10, Denver District Attorney Beth McCann announced Thursday. 

Dolloff was working as a contracted security guard for KUSA-TV at the time of the shooting. Keltner, a Navy veteran, was part of the pro-police "Patriot Muster" near Denver’s Civic Center Park when he got into a confrontation with a counter-protester moments before he was shot. 

Denver police identified Matthew Dolloff, 30, as the suspect in a fatal shooting that took place in downtown Denver during dueling protests. (Denver Police Department via AP)

Denver police identified Matthew Dolloff, 30, as the suspect in a fatal shooting that took place in downtown Denver during dueling protests. (Denver Police Department via AP)

A bystander tried to de-escalate the argument and Keltner appeared to pull out a can of pepper spray or Mace, according to a cellphone video taken by a KUSA-TV producer.

At one point, Kelter walks out of view of the video and a man appearing to be him gets angry at being filmed. 

“Get the cameras out of here or I'm going to (expletive) you up," the unidentified man says.

The recording stops for 12 seconds. 

Authorities said Keltner then got into a scuffle with Dolloff before slapping him in the face and using the spray on him. Dolloff then allegedly shot him dead. The cellphone video picks up as police secured the scene after the shooting.

Denver's medical examiner has ruled Keltner's death a homicide. 

Dolloff was contracted to work with the news station through the Pinkerton security firm, which sub-contracted him from another agency. The news outlet hires private security guards to accompany its staff to protests but has said it was not aware Dolloff was armed. 

Doug Richards, an attorney who said he represents the Dolloff family, previously said Dolloff acted in self-defense, The Associated Press reported. 

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Calls and emails to Richards from Fox News were not immediately returned. 

Dolloff faces up to 48 years in prison if convicted. The case against him will be filed in Denver District Court on Monday, McCann said.