Police have arrested a man only 24 miles from Washington, D.C. who allegedly had been plotting to carry out a mass shooting at his workplace.

Neil Prescott, 28, was arrested by police in Crofton, Maryland on Thursday night after he allegedly phoned in a threat to employer Pitney Bowes, a software and mailroom supplier, warning them that he would “shoot the place up.”

During a Friday afternoon press conference, investigator say that multiple threats were made several times over the course of multiple phone calls. When police conducted a field interview with the suspect, they say he was wearing a t-shirt that read, “Guns don’t kill people—I do.” Authorities say that, coupled with earlier information obtained in their probe, that “led us to a place where we could get an emergency petition” to arrest Prescott.

“If you call anybody and threaten to do harm — kill people — we’re going to believe you. And we did,” an officer involved in the investigation said during Friday’s presser.

Investigators say they found more than 20 firearms, including assault rifles, and 400 rounds of ammunition at his home.

According to authorities, Prescott identified himself as “a joker,” but they are not officially linking the planned shooting yet to last week’s incident in Aurora, Colorado. James Holmes, 24, is accused of opening fire at an Aurora cinema last week during a screening of the new Batman film and killing 12 people. Investigators say Holmes called himself the Joker, a reference to the comic book hero’s archenemies; he sported a hair-do similar to the sinister character’s own during his first public appearance on Monday.

A law enforcement source speaking with ABC 7 in Maryland says that authorities believe that, had they not foiled Prezcott’s plan, there “could have been another Aurora” only miles away from the nation’s capital.