CENTRAL ISLIP, N.Y. (CBSNewYork) — The Suffolk County district attorney says a pizza delivery driver with prior emotional problems threatened his former school and now is being held on a $750,000 bond after an arsenal of illegal assault weapons was found in his home.

Robert Csak, 32, of Lindenhurst, is facing multiple weapons charges after nearly two dozen firearms were recovered from his home, along with ammunition and an alarming cache of tactical gear.

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The charges stem from an investigation started when the Clarkstown Police Department went to check Csak after he alledgedly left a series of threatening voicemails, directed at an employee, on the answering machine of the Summit School in Upper Nyack on Saturday.

Csak wasn’t home when officers arrived, so police say his landlord let them into his house on 38th Street where they observed a tactical shotgun, crossbow, night vision goggles, high-capacity magazines, and an assault-style weapon.

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After securing the apartment and obtaining a search warrant, officers recovered an additional 19 firearms, a silencer, more than 200 high-capacity magazines, a Tommy gun, an additional set of night vision goggles, bulletproof vests, gas masks, knives, asps, and a bump stock.

Authorities say Casak was arrested while on the job late Saturday at a red light.

Csak attended the Summit School for youth with emotional and behavioral issues in 2002 and was identified through caller ID and school records, according to police.

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“From every indication we have now he felt slighted by this individual from an encounter back in 2002 and was carrying a grudge,” Suffolk Police Chief Stuart Cameron said.