Police Find Wig, Shawl and Gun in Virginia Shooter's Car

A briefcase with a wig, shawl and three license plates were among the items found inside the car of the gunman who killed two of his former colleagues during a televised interview in Virginia on Wednesday, according to a search warrant.

ABC News has obtained the warrant filed to search the rental car that Flanagan was using when he fled the Virginia State Police on Wednesday, following the shooting that left Alison Parker and Adam Ward dead.

Inside the Chevrolet Sonic, police found a Glock pistol, six ammunition magazines and ammunition for a 9mm weapon.

There were also 17 stamped letters, to-do lists, and "assorted handwritten & typed letters/notes," though the subject of the notes was not specified in the search warrant.

It was not clear what use items found in the briefcase -- the wig, shawl, a pair of sunglasses, an umbrella, and three different license plates -- were intended for.

The documents call Flanagan a "person of interest" in the case at the time, and were filed "based upon a text message sent to a friend making reference to having done something stupid."

Flanagan, who used the name Bryce Williams while working on air, refused to pull over for authorities on I-66, and when a trooper approached, he was found to have suffered a self-inflicted gunshot wound while in the car.

He was airlifted to a nearby hospital but died after he arrived there.

Also today, FBI Director James Comey renewed calls for the public to speak up when they see something suspicious.

"We'll check it out. If it's nothing, it's nothing, right? No harm done," Comey said. "But if it was something, you may have just stopped something horrific from happening."

Still, Comey said he doesn't know if Vester Lee Flanagan's rampage yesterday "could have been predicted" by law enforcement.

ABC News' Mike Levine contributed to this report.