The FBI is opening a domestic terrorism investigation into the shooting that killed three people and injured 13 others at a popular California food festival.

The gunman, Santino William Legan, killed three people, two of them children, and wounded 13 others with a Romanian-made AK-47 variant rifle at the festival before turning the gun on himself.

Describing Legan's ideology as "fractured," John Bennett said the FBI was continuing to dig through his online presence.

"He appeared to have an interest in variant, competing, violent ideologies," Bennett said.

Read more: USA Today