A firefighter is pictured trying to put out a blaze on Oct. 24, 2007. David McNew/Getty Images

A teenage firefighter in Pennsylvania who responded to a building fire on Monday was charged with arson after police said he confessed to starting the blaze.

Patrick Gillis, 18, was arrested after he told authorities that he "just wanted to respond to a fire," according to a police report.

Gillis was charged with arson, causing a catastrophe and intentionally destroying an unoccupied structure. He is in custody at the Allegheny County Jail where he remains on $25,000 bail. His preliminary hearing is scheduled for May 30.

The incident was reported around 4 p.m. in Allegheny County’s borough of Brackenridge. No one was injured.

The fire was intentionally set in the kitchen of the two-story building, the Allegheny County Fire Marshal’s Office determined. Damage to the building is estimated at $150,000, the Post-Gazette reported.

Witnesses told officers that Gillis was near the building before the fire started around 3:30 p.m. Later, he arrived on the scene as a firefighter for Pioneer Hose Company, where he volunteered.

A witness who lives across the street from the damaged duplex claimed to see Gillis near the property around 3:45 p.m.

Gillis previously volunteered as a junior firefighter with Highland Hose Fire Company, reported WTAE, an ABC affiliate in Pittsburgh.

Police questioned Gillis after they took him to the station, where he revealed that he started the fire by putting a lighter and some pieces of paper in a microwave before exiting the building, the report said.

Officials at the Pioneer Hose Company were suspicious of Gillis, whose name had been "brought up in recent nuisance fires in the area," the complaint said. He had previously at the same duplex.

"Once we got his number and realized it was his number, then we pulled him into our office and confronted him. Once he denied it, then we notified the fire marshal's office and said, 'Hey, we think we got something suspicious going on here,'" Fire Chief Rick Jones told police.

"We just had suspicions. Until you have proof, then you really don't want to act on it because you hate to do something like that to a young kid, you know."

Still, Gillis' mother, Dana Gillis, thinks he didn’t start the fire and that he only admitted to it because he felt pressured during police interviews.

“I’m a mother. You’re supposed to believe your children. What mother, what parent wouldn’t believe in their own children?" Dana Gillis told WTAE. "There was a window open, and I can’t see my son fitting through that window because he’s a big boy."