Texas ? An Army reservist at an Afghanistan detention center struck and taunted a detainee who may have been mentally disabled, a former soldier testified as a military trial began Thursday.

Former Spc. Jeremy Callaway told jurors that Sgt. Duane M. Grubb was one of two soldiers who repeatedly struck Zarif Khan while the detainee held on to barbed wire in a cell.

Callaway also said Grubb, of the Cincinnati-based 377th Military Police Company, was among four troops who taunted Khan, calling him “Timmy,” in reference to a disabled character on the cartoon “South Park.” Khan has been described as mentally retarded.

Grubb, of the Cincinnati-based 377th Military Police Company, is the sixth Ohio-based reservist to be court-martialed in an abuse investigation prompted by the deaths of two other detainees at the Bagram facility in 2002. He has pleaded not guilty to charges of assault, maltreatment and making a false official statement.