A 32-year-old pizza deliveryman still harboring a grudge against his high school was found with a weapons arsenal — including a bump stock similar to the one used in the Las Vegas massacre — in his Long Island home, authorities said.

Suffolk County cops raided the home of Robert Csak on Saturday after he left a threatening voicemail against Summit School in Upper Nyack earlier in the day, law enforcement said. Csak attended the school in 2002.

Authorities recovered a shotgun, crossbow, night-vision goggles, Tommy gun, silencer, bulletproof vests, gas mask and high-capacity magazines in his Lindenhurst home, police said. Also among the items was a bump stock like the one used by the gunman in the Vegas massacre in October, police said. The bump stock is used to create automatic fire with a semi-automatic weapon.

Police went to Csak’s home after they received the tip from the school.

Csak was arrested by police and charged with 17 counts of possession of a weapon.

He is scheduled to be arraigned in Central Islip on Monday.