The man shot at the Democrats' office in Tempe outside Phoenix on three separate occasions, two in September and one in October.
During a search of the 60-year-old's home, more than 120 weapons and over 250,000 cartridges were found, leading the police to suspect that he was planning a mass shooting.
Some of the weapons were submachine guns, according to the police. They also found a grenade launcher, telescopes, bulletproof vests, and silencers. An automatic weapon was also found in the man's car.
Outside the shooter's house, he had placed signs with anti-democratic messages framed with razor blades. According to the authorities, plastic bags with white powder marked "biohazard" were hanging from the signs. His Facebook page was also filled with hateful messages about the Democrats and the party's presidential candidate Kamala Harris.
No one was present at the campaign office in Tempe when the shots were fired. The office has since been closed. The man, a retired flight engineer, is now being held on suspicion of several serious crimes.
Arizona is one of the swing states where the presidential election on November 5 is expected to be decided. The election campaign has been marked by violence, including two attempted murders of the Republican candidate Donald Trump.
