as deputies closed in, investigators believe the final shots were 57-year-old samuel cassidy taking his own life after killing nine coworkers. we immediately go in. this protocol, i believe, saved lives. there were over 100 people in that area. he had a lot of additional ammunition. reporter: but no one has been able to answer the most pressins question: why did this happen? jamie yuccas, cbs news. o donnell: and tonight, the manhunt for three gunmen who opened fire on a concert crowd near miami may be expanding to more possible suspects. we get the latest now on the investigation from cbs manuel bojorquez. reporter: tonight, a closer look at surveillance video reveals the possibility of an additional shooter or shooters in the attack that killed two people and injured 21 after a rap concert sunday. miami-dade police previously released this video of the s.u.v. used in the shooting, and