Authorities said the structure fire caused significant damage to the building and evidence inside.
Police responded to the fire after a driver in a passing car reported smoke coming a building at about 2:20 a.m. Monday. Firefighters arrived in less than two minutes and stormed the building to fight the fire.
Authorities immediately thought the fire was related to the other attacks on the city because it was a city building, and those thoughts turned to fear when they heard ammunition going off all around them.
"Certainly, our crews responding to a scene have that in the back of their minds as they get ready to go into the building and extinguish the fire," said Hemet Fire Chief Matt Shobert.
Fortunately, the ammunition going off was merely evidence that was stored at the facility, and no one was hurt.
Still, for police there's no sign that they're any closer to catching the suspect or suspects, which leaves city officials on edge.
"You can't live on that edge all the time," said Lt. Duane Wisehart of the Hemet Police Department. " Every shift you go to, you don't know what's going to go on, what's going to happen in the parking lot, to the building, to your car. That's a lot to ask for somebody."
Gas lines have been rigged to blow up, booby traps have been set, dangerous devices have been planted on police cars, city trucks have burned, a fire was set at a police shooting range and a couple weeks ago, there was even a bazooka missile found on a nearby rooftop.
"People are intentionally trying to cause harm," Shobert said. "It really provides difficulty for us as first responders."
Hemet police have already arrested 23 people, some for parole violations, after a probe into the attacks.
Police say it's only a matter of time before the suspects are caught, before one of these booby traps becomes deadly.
"Eventually someone's going to be hurt, whether it's a firefighter trying to put out a fire or something like that, that's probably not the target, but we don't want anyone getting hurt," Wisehart said.
Anyone with information is urged to call the Hemet Police Department's tip line at (951) 765-3897. A $200,000 reward is being offered for anyone with information leading to an arrest and conviction.