By: Jennifer Pierce OKLAHOMA CITY - A metro security guard is under investigation by multiple law agencies following a weekend shooting in downtown Oklahoma City. Police arrested Antjuan Martin, 48, on Friday after he allegedly shot a homeless man during an altercation. News 9 obtained cell phone video of the scene at Taco Bell near Sheridan Avenueand Classen Boulevard. The victim was on the ground in the parking lot, and it appeared Martin was walking the scene. Police said it all started when Bradley Bishop, 25, refused to leave the restaurant. “An altercation ensued between the two and at some point, the security guard unholstered his weapon and fired several times as the individual was walking away,” said Sgt. Dillon Quirk with the Oklahoma City Police Department.