A civilian employee set a fire that caused $400 million in damage to a Navy submarine because he was suffering from anxiety and wanted to get out of work early, Navy investigators said in a complaint filed Monday.

Casey James Fury, 24, of Portsmouth, N.H., faces up to life in prison if convicted on two counts of arson for allegedly setting fire to the USS Miami nuclear-powered attack submarine while it was in dry dock on May 23, and setting a second fire outside the sub on June 16.

Fury was taking multiple medications for anxiety and depression, and told investigators he set the fires so he could get out of work, according a 7-page affidavit filed in U.S. District Court in Portland on Monday.

Fury, who was working on the sub as a painter and sandblaster, initially denied starting the fires, but eventually acknowledged his involvement, the affidavit reads. He admitted to setting the May 23 fire, which caused an estimated $400 million in damage, while taking a polygraph test and being told by the examiner he wasn't being truthful.

"The reason he set the fire was in order to get out of work," the affidavit reads. "Fury further explained to (the examiner) that he had failed to admit his involvement...because he was scared and because everything was blurry to him and his memory was impacted due to his anxiety and the medication he was taking at the time."

The Miami was in dry dock at Portsmouth Naval Shipyard in Kittery, Maine, for an overhaul when the fire broke out May 23, damaging the torpedo room and command area inside the sub's forward compartment. It took more than 12 hours to extinguish the fire.

A second fire was reported June 16 on the dry dock cradle on which the Miami rests, but there was no damage or injuries.

Fury denied involvement in the fires when he was interviewed the day after the first fire and two days after the second fire, according to the affidavit from NCIS agent Jeremy Gauthier.

At a follow-up interview last Wednesday, Fury told Gauthier he set the second fire after getting anxious over a text conversation with an ex-girlfriend about a man she had started seeing, according to the affidavit. Fury described how he wanted to leave work early, so he took some alcohol wipes and set them on fire outside the submarine.

Fury eventually admitted to setting the May 23 fire after agreeing to take a polygraph examination on Friday. When the polygraph examiner told Fury he wasn't being truthful in denying his involvement in the fire, Fury admitted he had caused the fire, the affidavit said.

Fury told Timothy Bailey, the polygraph examiner and a NCIS agent, that "his anxiety started getting really bad" so he grabbed his cigarettes and a lighter, walked up to a bunk room and set fire to some rags that were on the top bunk before returning to work.

The Navy originally said the fire started when an industrial vacuum cleaner sucked up a heat source that ignited debris inside the vacuum.

Fury told Gauthier that he was taking three medications for anxiety, depression and sleep, and a fourth for allergies. He checked himself into an in-patient mental health facility on June 21 and checked himself out two days later, the affidavit reads.

If convicted of either charge, Fury could face life imprisonment and a fine of up to $250,000 and be ordered to pay restitution, the U.S. Attorney's Office said. Fury was scheduled to make his initial court appearance Monday afternoon.

Federal Public Defender David Beneman, who represents Fury, declined to comment.