DENVER (CBS4) – Matthew Dolloff, a security guard, was officially charged with second degree murder on Monday. Prosecutors say Dolloff shot and killed Lee Keltner during dueling protests in Denver on Oct. 11.

(Photo by Helen H. Richardson/MediaNews Group/The Denver Post via Getty Images)

Dolloff was working as a security guard for KUSA-TV. A shouting match ensued as the protests were ending.

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Matthew Dolloff (credit: Denver Police)

According to the probable cause statement released by the Denver Police Department, Dolloff got involved in the altercation with Keltner and another protester before Keltner hit Dolloff on the side of the head with an open hand.

(Photo by Helen H. Richardson/MediaNews Group/The Denver Post via Getty Images)

During the argument, Dolloff pulled out his handgun and fired one shot at Keltner.

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Keltner, who sprayed pepper spray toward Dolloff, died.

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In an interview with the Colorado Sun, Dolloff’s lawyer says his client was acting in self-defense.

Danielle Chavira