>> become orderly. we're taking everybody a little furtherary way from the front of this building all right? >> reporter: a deadly scene in a dallas suburb. two gunmen shot dead after opening fire and wounding a security guard outside an event center where a cartoon drawing contest of the prophetmohammed was being held. law enforcement officials tell cnn the entire shooting lasted about 15 seconds. >> we prepared for something like this. >> reporter: the security officer, bruce joyner was treated at the hospital for an ankle gunshot wound and released. this video shows the moment gunfire erupted, an interview with the president of the organization sponsoring the event cut abruptly short as security rushed the scene. >> sorry, we've got to stop this right now. >> shots fired. >> shots fired. >> shots fired. >> reporter: witnesses describe the chaotic turn of events. >> there were military or policemen everywhere running. >> sounded like boom, boom.