A couple more facts: One of the two thieves was a former tenant of Mr. Sokolowski who knew about the guns in the basement bunker and also knew that Mr. Sokolowski had moved out... leaving the thieves all the time in the world to break open the bunker door and steal the guns.
That's what pissed off the Lowell cops so much: The idea that the guns were left there unguarded after the owner had moved out... fully known to the shady dude who then set the theft in motion.
The cops couldn't charge Mr. Sokolowski just for leaving the guns unguarded, so they had the fire department charge him with not having a permit for his reloading supplies. It was a total shit move by the cops, but they were pissed.
When they can't get you one way, they figure out a way to get you another way.