 and will share the results of that independent review with the American people as well. The FBI still doesn't have a motive, but has learned where that shooter got an AR-15-style weapon. CBS's Nicole Skanga. ATF and FBI traced that weapon back, found that it was legally purchased by the suspect's father. In addition to that, law enforcement finding materials described as incendiary or explosive in his vehicle and some sort of mechanism on his person that is thought to trigger those materials.