The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives confirmed the investigation but declined to elaborate.
Court documents connect Capt. Harold Kelley of the Liberty County sheriff's department and others to a gun-trafficking scheme. As custodian of the police department's evidence room, Kelley possessed one of two keys. The other key was held by Henry Patterson, who was serving at the time as Cleveland's assistant police chief.
ATF agents recovered 112 missing guns during a search at a Humble gun shop, according to court documents. Of those weapons, 98 had been listed by Kelley as destroyed. The whereabouts of the other guns remains a mystery.
Among the missing weapons are several 12-gauge shotguns, Glock pistols and revolvers.
The Texas Rangers, which had been looking into the missing weapons, found the sale of the weapons to a gun shop "suspicious and irregular," according to the court documents.
Generally, Texas law enforcement departments destroy contraband firearms themselves, using smelters, crushing machinery and shredders, the court documents said.