Yeah, a car is a big place. You need help to find a weapon in a big place like a car.
Apparently these super-cops did. It must have been one big car! Check this out from CNN:
"Indiana police found two other guns along with the Glock that investigators said was used to kill the Bordens -- a Ruger .45-caliber semiautomatic pistol and a Ruger .223-caliber mini-rifle -- and ammunition inside the car. A second search two days later also turned up a Colt .45-caliber pistol, 45 bullets and a holster, the documents state."
Took a second search to find that tiny Colt .45 and 2 boxes o' ammo. So small and such a big car... I can see how they'd miss 'em in the first search.