Police in Maryland have arrested suspect who referred to himself as "a joker" and threatened to shoot up his workplace, investigators said Friday.

An official with knowledge of the investigation told The Associated Press that Neil Prescott of Crofton, Md., phoned in the threat to software and mailroom supplier Pitney Bowes near Washington, D.C. Investigators say a search of Prescott's home turned up more than 20 guns, including assault rifles and handguns, and more than 400 rounds of ammunition.

The official spoke on condition of anonymity because the investigation is unfolding.

Though the suspect referred to himself as "a joker" when he called in the threat, the official said there is no other known connection to a deadly shooting last week at a Colorado movie theater during the latest Batman movie.

Investigators believe Prescott , who was arrested Thursday night, had lost his job with the company and was disgruntled. They say he called in the threat earlier this week.

A message left at a telephone listing for Prescott in Crofton was not immediately returned.

Prescott was being held Friday at Anne Arundel Medical Center in Annapolis, where he was undergoing a psychological evaluation. Crofton is located between D.C. and Annapolis, Md.

A message left for a corporate spokeswoman at Pitney Bowes seeking comment was not immediately returned.

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Associated Press writer Jessica Gresko contributed to this report. Tucker reported from Palmer Park, Md.