PORTLAND — A civilian shipyard worker accused of setting a fire that caused $400 million in damage to a nuclear-powered submarine will remain in jail after a magistrate ruled Wednesday that the defendant is too great a risk to society and a Navy officer described a harrowing scene inside the burning vessel.

Casey James Fury, 24, of Portsmouth, N.H., faces two counts of arson at the Portsmouth Naval Shipyard, charges that carry a sentence of up to life in prison.

The Naval Criminal Investigative Service says Fury confessed to setting a fire inside the USS Miami while it was in dry dock May 23, setting a second blaze outside the sub on June 16 and later setting off a fire alarm.

“There’s no question that the offense in this case is of the utmost grave order,” Magistrate Judge John Rich III said.

During the hearing in U.S. District Court, Fury’s lawyer suggested that he could be released to live with his father and stepmother in Eliot, Maine, while awaiting trial. The attorney, David Beneman, likened the case to a middle school student who pulls a fire alarm hoping to get out of a test, only the ramifications turned out to much more severe.

Rich, however, agreed with federal prosecutors that the only way to ensure the public’s safety was to keep Fury in custody. He said he was especially concerned that the defendant allegedly went on to set the second fire after the first caused so much damage.

Fury’s father and stepmother left the courthouse without comment after the magistrate’s ruling.

Fury, a painter and sand blaster, told Navy investigators that he set the fires to get out of work because he was suffering from anxiety and having problems with his girlfriend.

Brett Boley, an NCIS special agent, said Wednesday that Fury walked investigators through the Miami and another Los Angeles-class sub, demonstrating where he’d set fire to rags on a bunk bed before returning to his post in the forward torpedo room.

The blaze quickly got out of control and the steel hull trapped heat, causing superheated smoke and a stubborn fire that took more than 100 firefighters to douse.

The submarine was undergoing a 20-month overhaul at the Navy shipyard in Kittery, Maine. The fire was confined to forward compartments and did not reach the back of the submarine where the nuclear propulsion components are located.

It remains to be seen if the attack sub will be repaired or scrapped. A Navy spokesman said Wednesday that there was no further word on the sub’s future.

Lt. Richard McMunn, an officer aboard the sub, testified Wednesday that he had just completed his shift and was taking off his boots when he learned of the May 23 fire alarm.

As he climbed down a hatch into the inferno, “I felt that I was climbing down the chimney of a furnace,” he said. “Black smoke was billowing up.”

At the bottom of the ladder, McMunn said he fell five to six feet in the darkness, breaking six ribs, injuring his knee and realizing that he might die. With only 20 minutes of oxygen left, he ended up having to rescue himself and endured excruciating pain as he slowly climbed the equivalent of a two-story ladder to get out of the sub.

“I come to you today as a fortunate man. Unlike the victims of similar crimes, I’m still alive,” he said.

Fury told the NCIS that, less than a month later, he used alcohol wipes to set the second fire underneath the submarine after a text-message exchange with an ex-girlfriend, Boley said. That fire, which was set two days after Fury was arrested for driving under the influence in New Hampshire, ended up causing little or no damage.

Three days later after that, Fury set off a fire alarm, investigators revealed Wednesday.

Fury told the NCIS that he was taking medications for anxiety, depression and insomnia and that he felt that his boss wouldn’t let him leave work because his medical leave had been used up.

Now using new medication, with a stint at an in-patient mental health facility under his belt and terminated from his stressful job, Fury is not a threat to the public, Beneman argued. A U.S. probation officer agreed that arrangements could be made to satisfy concerns about public safety and to ensure Fury shows up for trial.

But the prosecution contended Fury was still a risk.

Assistant U.S. Attorney Darcie McElwee said the severity of the first fire may have come as a surprise to Fury, but then he proceeded to set a second fire.

“The second fire tells the whole story,” she said.

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