From the article, "Benn has a concealed handgun permit and has no criminal convictions, according to a 2009 renewal of his permit".
Also from the article...
Benn's statement is at odds with information released by police, who gave the following account: Benn accused Colorado of cutting in front of him and they began arguing just after 2 p.m. Colorado sprayed Benn with pepper spray. Benn then drew a handgun and approached Colorado, firing at him. Colorado drew a handgun, returned fire and collapsed.
Even if the police version is true, it still sounds like self defense to me.
The police version has Colorado initiating the argument by cutting in line and then pepper-spraying Benn. But, it also has Benn drawing first and advancing on Colorado, which would undermine the self defense argument. Benn says he drew after Colorado started to go for his gun.
No disrespect intended to the police, but they may be erring on the side of arrest because the initial info is that Colorado had some minor law enforcement association.