The story comes via Instapundit...
Knox County (TN) Commissioner Greg Lambert hears a commotion at the shopping mall, cries that someone had been shot. Two unarmed security guards are trying to respond. Luckily Lambert is a CCW carrier, so when they find the armed suspect he holds him for police. As they arrive, the perp apparently tries again to start firing and they put him down.
The linked articles say the perp killed a store clerk because he was unhappy about a purchase, and was shot and wounded.