The co-owner of United Gun Shop in Rockville, Maryland, says 18-year-old Darion Aguilar—who purchased a 12-gauge shotgun at the store, then used it to kill two people and himself in a nearby shopping mall—"was an ideal customer."

Cory Brown, one of the shop's proprietors, told the Washington Post that Aguilar's "whole demeanor was, he smiled, he was polite, he wasn't aggressive" as he asked to look at a Mossberg shotgun he'd been researching:

So they got out a basic 500 model — "an entry-level" gun, Brown said — a pump-action 12-gauge that is easy for a novice to fire accurately in close quarters.

Saturday morning, 46 days ­after he left the shop with a $430 Mossberg 500 and two boxes of shells, Aguilar used the weapon at the Mall in Columbia, killing two employees of a clothing store and then himself as hundreds of frightened shoppers ran for cover.

"This guy, to rate him as a customer, he was an ideal customer," Brown said Monday at his store off Randolph Road. "We get plenty of people that come in here and look shady. We turn them away. We don't even bother doing the paperwork. But this guy asked a lot of good questions. All 'please' and 'thank you.' Engaged us great.

The gun shop's proprietors puzzled over what drove Aguilar to use his gun as a murder weapon, since he "asked lots and lots of questions, all the right stuff"—the teen, who was old enough to buy a shotgun but not a pistol, said it was for "home defense." But Brown did concede that Aguilar's shotgun was easy to break down and modify for close-quarters use:

He easily could have disassembled the 35-inch-long Mossberg beforehand, stashed the parts in his backpack and reassembled them in the dressing room, Brown said.

"Very quickly," he said "All it takes is a simple screwdriver."...

When investigators found the weapon near Aguilar's body, they said, it had a pistol grip, though it didn't have one when he purchased it.

"We don't sell them," Brown said. The gun had a conventional stock. "One screw, though, the stock comes off, and it's a $10 grip you just stick on there."

Brown said he turns lots of "crazies" away from the store all the time, but he bore no reservations about the sale to Aguilar. "His whole context was home defense," Brown told the paper. "He was new to this. He wanted something not too crazy — he didn't ask about [assault] rifles; he didn't ask about handguns." It's true: You never can tell who might have a killing impulse. The only thing you know for certain is, a Mossberg 12-gauge with buckshot would certainly be one way to indulge it.

[Photo credit: AP]