Authorities have arrested a Maryland man they say referred to himself as "a joker" and threatened to carry out a shooting at his workplace.

Police arrested 28-year-old Neil Prescott of Crofton, Md., after he allegedly called his employer and threatened to "shoot the place up," a source close to the investigation told Fox News.

Authorities say the suspect called himself "a joker" before his arrest Thursday. Officials say they believe the threat could have been carried out as a copycat of the shooting massacre one week ago in Aurora, Colo., in which 12 people were killed and 58 injured during a midnight viewing of the new Batman film "The Dark Knight Rises."

"I am a joker. I'm gonna load my guns and blow everybody up," the man told his supervisor in a phone conversation earlier this week, officials said.

The suspect was also wearing a T-shirt that said, "Guns don't kill people. I do," when taken into custody, according to authorities.

During a press conference Friday afternoon, authorities referred to the case as a "thwarted terror threat" and called it "significant."

"We can't measure what we prevented here," Prince George's County Police Chief Mark Magaw told reporters Friday. "We averted a significant...and violent episode."

Police said that when they took the man into custody, they found an "arsenal" of weapons inside his home. The Associated Press reports that a search of the suspect's home turned up more than 20 guns, including assault rifles and handguns, and more than 400 rounds of ammunition.

The man was about to get fired from his job at Pitney Bowes, a software and mailroom supplier in Prince George's County, authorities said. He was arrested at his home in Crofton, Md., Thursday night.

Pitney Bowes spokeswoman Carol Wallace said in an emailed statement to the Associated Press that Prescott was an employee of a subcontractor to the company and had not been on any Pitney Bowes property in more than four months.

A source told Fox News that Prescott is "emotionally disturbed." He was being held Friday at Anne Arundel Medical Center in Annapolis, where he was undergoing a psychological evaluation. Crofton is located between Washington, D.C., and Annapolis, Md.

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Fox News' Mike Levine and the Associated Press contributed to this report.