unloading into the army. >> the fbi has taken over the case. so far, there's no clear motive, but the attack is being investigated as domestic terrorism. well, new details are emerging about the suspect, said to be a naturalized u.s. citizen from a middle-class muslim family. investigators say he appears to have been the lone gunman and looks like he hadn't raised any previous red flags. here now, abc's pierre thomas. >> reporter: the fbi's identifying the suspect as muhammad youssef abdulazeez shown here in a mug shot from a drunk driving arrest earlier this year. he is 24 years old and sources say born in kuwait. authorities are now investigating if he was inspired by isis or another terrorist organization. sources tell abc news this man was not under active surveillance by the fbi, a classic, so-called lone wolf. the suspect wrote in his 2008 high school yearbook that "my name causes national security alerts. what does yours do?" we've learned the 24-year-old was an electrical engineer with a good-paying job, a recent grad