KITTERY, Maine (WHDH) -- A New Hampshire man working as a painter at the Portsmouth Naval Shipyard has been charged with starting a fire that caused $400 million in damage on a nuclear-powered submarine.

The late May fire on the USS Miami was so devastating, seven people were hurt and it took crews more than 12 hours to put it out.

The civilian painter charged with arson allegedly confessed to investigators he set the fire because he wanted to leave work early.

About a month after the May incident, there was another smaller fire inside the same sub. That fire didn't cause much damage, but investigators soon learned the cause was someone setting fire to alcohol wipes.

That second fire raised more red flags, and according to the affidavit, investigators interviewed people who were on the docked submarine for both fires.

The attack sub is undergoing a 20-month overhaul while docked in the Portsmouth Naval Shipyard.

The court paperwork reveals a painter from Portsmouth was questioned about the June fire. At first, he denied any involvement. Later, he allegedly confessed to setting that fire-because, “He became anxious over a text conversation with his ex-girlfriend and wanted to leave work.”

The paperwork reveals the suspect then agreed to take a polygraph test about the first fire and failed the lie detector test.

According to the affidavit, he confessed to investigators he started both fires-both times because he wanted to leave work early.