TEMPE, Ariz. —

An Arizona prosecutor said the man arrested in the shooting of a Democratic National Committee office in suburban Phoenix had more than 200 guns and over 250,000 rounds of ammunition in his home, leading law enforcement to believe he may have been planning a mass casualty event.

Maricopa County prosecutor Neha Bhatia said at Jeffrey Michael Kelly’s initial court appearance on Wednesday that federal agents told her about the large seizure made after Kelly’s arrest. Scopes, body armor and silencers were also found, she said. A machine gun was discovered in the car he was driving.

The sheer size of the cache led authorities to believe “this person was preparing to commit an act of mass casualty,” Bhatia said.

Police said Kelly, 60, allegedly fired BB pellets and then gunshots at the glass front door and a window of the Arizona Democrats’ field office in Tempe. Police found three .22 caliber bullet casings while searching Kelly's trash, according to court documents.

Nobody was inside during the shootings in the early morning hours of Sept. 16, Sept. 23 and Oct. 6.

Kelly is also accused of hanging several political signs lined with razor blades on Tuesday in Ahwatukee, an affluent suburb of Phoenix where most voters have chosen Democrats in recent elections. Authorities said he also hung plastic bags holding a white powder labeled “biohazard” from those signs.

Authorities said the hand-painted signs were attached to palm trees and appeared to criticize Democrats and their presidential nominee, Vice President Kamala Harris.

Kelly was being held on three felony counts of acts of terrorism and four other counts related to the shootings, according to police. A $500,000 cash bond was set with a requirement for house arrest and an ankle monitor in the event he is able to raise that amount.

His attorney Jason Squires said Kelly was a retired aerospace engineer who at one time had top security clearance, had no criminal record and was not a flight risk.

Kelly’s next appearance was set for the morning of Oct. 29 in Maricopa County Superior Court.

The Tempe location was one of 18 Harris field offices in Arizona where Democrats gathered to organize Harris campaign efforts. It was shut down after the last shooting, police said.

Arizona is one of the battleground states where the competition between Harris and former President Donald Trump has been particularly intense.

Political violence has already marred the campaign season, with the Republican presidential nominee being targeted by assassination attempts at a campaign rally and at one of Trump's Florida golf courses.