First a startling discovery: Published reports that the shop's owner cannot account for more than 300 guns sent to his store.
The Seattle Times reports that federal investigators cannot account for 340 guns at Bull's Eye Shooter Supply -- including the sniper's rifle.
But, owner Brian Bobrgelt told KOMO 4 News that figure is "irresponsible" -- he says it's just not true.
And, federal sources told KOMO 4 News more about what may have happened to the sniper's gun.
Federal agents know the gun was shipped to Bull's Eye last June -- a Bushmaster XM 15 assault rifle.
KOMO 4 News has learned that even though agents can't find the gun, they did find the empty box at the store.
And so far, they've found no record of the rifle's sale.
So, sources tell KOMO 4 News that agents are now investigating whether the gun could have been shoplifted or sold without documentation.
They also say the Bushmaster rifle was a display model: on the rack for customers to see and handle.
It was equipped with a scope and bi-pod.
When police searched John Muhammad's car, they found a scope and bipod, with the rifle.
Is it likely Muhammad or anyone else could have simply walked off with the gun? One customer recently bought a rifle at Bull's Eye. He says the staff was vigilant, but very busy.
"When I went in there, they keep an eye on things," Brian, a customer at the store said. "But then again, I think it would be really easy to walk out of there with a firearm. When I was in there they'd have a lot of them out to handle."
But gun shop owner Scott Peskin thinks shoplifting would be difficult.
"I couldn't imagine it getting that busy where you would have guns walking out the door," he said.
He says most shopkeepers avoid putting a lot of guns on the counter, and they show only one at a time.
"So it doesn't get confusing, so somebody can't put a bullet in it and hold up the shop, or run out the door with one," Peskin said.
As for the 340 guns that may be missing from Bulls Eye, Peskin says the shop has a good reputation.
"I couldn't imagine that many guns being gone. (That would be) very highly unusual."
One employee at Bulls Eye told KOMO 4 News that "if we had 340 guns missing we'd all be in handcuffs and out the door."
In the meantime, the ATF is continuing its audit, which includes a careful comparison of the shop's inventory with its records of sales.
Agents say it's one of the largest gun shops in Washington, and the work may take some time.