I'm not sure if it is a requirement, but my understanding was that most if not all of the violence interrupters are convicted felons who have served time for violent felonies -- a mark of distinction that purportedly gives them the "street cred" to interact with people who are thinking about committing criminal violence.

If the violence interrupter involved in this shooting was a convicted felon, he/she was disqualified from owning/possessing firearms. Surely he/she was not eligible to obtain a DC concealed carry permit.