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DENVER (KDVR) — A 9NEWS contracted security guard, Matthew Dolloff, 30, is the suspected shooter in a deadly incident that happened after a dueling rally event, killing 49-year-old Lee Keltner on Saturday.

On Tuesday morning, FOX31 picked up the official arrest affidavit for Dolloff.

The court documents explain what led up to the shooting of the victim, Lee Keltner.

At around 3:30 p.m. Saturday, Keltner began walking southbound from Civic Center Park after attending an organized rally.

Uniformed officers from the Denver Police Department, Arapahoe County Sheriff’s Office and Douglas County Sheriff’s Office were on scene for crowd control, according to the document.

According to the arrest affidavit, while walking, Keltner and a man got into a verbal dispute. Both men yelled and postured, leading several witnesses to believe the men may engage in a physical altercation. The dispute was captured on Denver HALO cameras, as well as cell phone video and digital photography from multiple witnesses

Read: The victim: Lee Keltner

The documents go on to explain what a review of the video and still images showed. A man and Matthew Dolloff become engaged in an altercation with Lee Keltner while he was arguing with another man. At this time, Keltner was observed holding a can of OC spray. At 3:36 p.m., Keltner turned his attention toward the other man and Dolloff. Keltner and Dolloff faced each other and Keltner struck Dolloff in the side of the head with an open hand. Dolloff is observed drawing a handgun from his waistband, aiming at Keltner and shooting once, striking Keltner as he discharged the OC spray. After which he collapsed to the ground. All of this, according to the official arrest documentation released Tuesday morning.

Dolloff was arrested on scene. Keltner was taken to the hospital where he was pronounced dead.

Problem Solvers learned that Dolloff was being held in isolation away from other inmates for his own protection and without bond for investigative hold on a count of first-degree murder.

While one man says he witnessed a murder right in front of him, an attorney for the Dolloff family says he felt threatened.

FOX31 asked a local attorney what constitutes self-defense and if Dolloff would be able to claim the reason.