Police said they saw a 25-year-old Bellevile man taking a television through a motel window when they approached him on Sunday in Caseyville.
Officers approached Philip A. Ney and another man in a car parked at the America's Best Inn after seeing them load the stolen TV, according to a news release.
The man who had taken the television didn't want to get out of the car and was reaching behind him, police said, so they removed him from the car and detained the man.
Police said they found a loaded .22-caliber Ruger pistol with a sawed-off barrel on the suspect, who was a convicted felon.
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Ney was charged with unlawful possession of a weapon by a felon. It is a class 3 felony. He was in custody at St. Clair County Jail on Thursday with bail set at $35,000.
Cutting the barrel of the handgun is not illegal, said Caseyville Police Chief Tom Coppotelli.
"On a pistol, it's different than a rifle or a shotgun. Unless you deface the serial number, you can alter it. ... We can only assume for easier concealment," Coppotelli said.
Police said the suspect gained access to the room because an acquaintance had rented it.
The other man in the car was not charged.