Update: FBI Received Tip to Investigate Oregon Teenager

WASHINGTON (AP) — A law enforcement official says federal agents began investigating the suspect in the Christmas tree bombing plot in Portland, Ore., after receiving a tip from someone who was concerned about the teenager.

The official tells The Associated Press that Mohamed Osman Mohamud was acting on his own — without any instruction from a foreign terrorist organization.

The official was not authorized to discuss the investigation publicly and spoke on condition of anonymity.

The official said Saturday that Mohamud hatched the plan on his own to use a cell phone to detonate what he believed was an explosive-filled van at a crowded Christmas tree lighting ceremony Friday.

The official said Mohamud alone planned the details, including where to park the van for the maximum number of casualties.