THE COLONY (CBSDFW.COM) – Friends and family are still trying to understand what led to the fatal shooting of a North Texas veteran. This morning the man accused of killing former Army combat medic and drill sergeant Chandler Davis is his own brother.

John Davis III has been moved from the jail in The Colony to the Denton County Jail. The 38-year-old is charged with murder.

Chandler Davis died Sunday. Investigators in The Colony said the shooting happened after an argument over a gun.

People may not have remembered his name, but Chandler Davis’ face became known after a heartfelt display of compassion last summer. Pictures of the 34-year-old were shared across North Texas, and the country, as he stood at attention dressed in full uniform, in the heat, outside the Dallas Police Department as a tribute after the July ambush of police officers in downtown.

His best friend, Ashton Pennington, told CBS 11 News that those photos symbolized the kind of person Chandler was – respectful, honest, and an all around good guy.  “That’s the way… the kind of guy he is. He didn’t want to sit there and talk about it. He actually did it.”

Pennington said there was a little tension between the brothers at times, but it’s hard to imagine how something could escalate to murder. Chandler’s girlfriend, Elizabeth Rowe, agreed and said while the brothers had their differences, no one could have imagined an argument ending in this way.

Rowe now holds on to the memories of her time with Chandler. “He was one of those people who would give you his last penny,” she said. “He touched so many lives… more than I even realized.”

According to an arrest affidavit, the argument began because Chandler thought John had stolen one of his guns. Investigators believe John started to record their argument on his cell phone and when Chandler took the phone away John shot him. Three shell casings were found near Chandler’s body.

John told investigators he shot his brother because he “feared for his life.” When asked why he thought he was in danger he said Chandler “was threatening to break his cell phone and destroy the evidence that was on it.”

John Davis is being on a $100,000 bond.