Private security guard Matthew Dolloff is taken into custody following a fatal shooting during competing political protests in Denver on Oct. 10, 2020. (CBS4)

Prosecutors plan to drop a second-degree murder charge against a former television station security guard who shot a pro-police demonstrator following protests in downtown Denver in 2020.

Matthew Dolloff’s attorney, Douglas Richards, said the Denver District Attorney’s Office informed him by phone Thursday that prosecutors would dismiss the charge at a pre-trial hearing March 21.

“They just said they don’t believe they can prove the case beyond a reasonable doubt based upon the evidence,” said Richards, who declined further comment.

Carolyn Tyler, a spokeswoman for the district attorney’s office, said prosecutors had informed the family of the 49-year-old victim, Lee Keltner, that the case would be dismissed.

“In line with our ethical obligations, we cannot overcome the legal justifications of self-defense or defense of others,” she said in an emailed statement.

Dolloff was hired by KUSA-TV to protect a producer covering the Oct. 10, 2020, “Patriot Muster” demonstration and “BLM-Antifa Soup Drive” counterprotest.

Police say Keltner was arguing with a Black man as the rallies broke up before getting into an altercation with Dolloff.

Keltner slapped Dolloff in the head, and Dolloff pulled a handgun and shot Keltner as Keltner fired pepper spray at him, according to an arrest affidavit. A cellphone video taken by KUSA’s producer suggests Keltner was upset that his initial dispute was being recorded.