"He's not a firefighter, he would like to be a firefighter, he is interested in firefighting, he is interested in fires," U.S. Attorney Laurie Magid said.
Last year, Gilliam was arrested for stealing for motorcycles.
Investigators say he fits the classic profile of a firebug.
He tried to join the West Bradford Fire Company last month and was rejected.
Investigators say he bought his own firefighting gear and outfitted his car with strobe lights.
Gilliam is charged with setting a fire to the Happy Day's Family Bistro in Thorndale on the morning of January 25.
RELATED: More information on the arrests of Gilliam and Barlow.
The fire was hours after 15 homes went up in flames on Fleetwood Street in Coatesville.
Police say Gilliam returned to the diner and told investigators he was a firefighter and had been up all night working the Coatesville fire.
Police say Gilliam also led a State Trooper on a high speed chase two weeks ago, after someone reported a suspicious vehicle in a parking lot.
The State Trooper crashed and the chase ended.
When police searched Gilliam's home yesterday, they found fire starting materials and other evidence, including a stolen license tag that had been on Gilliam's car the night of the chase.
Police have charged Gilliam's friend Roger Barlow with setting 9 of the Coatesville fires.
Barlow initially told investigators that he would pick up Gilliam at his house and they would drive to Coatesville with a duffle-bag full of flammable liquids, rags, and cigarette lighters.
Barlow later retracted that statement.
"He has made statements, he has recanted portions of them, but everything in his statement is still something that we are looking at and investigating in other ways," Magid said.
This is an ongoing investigation.
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