An Oklahoma couple arrested in the 2006 disappearance of their 9-year-old nephew had beaten the boy until he lay motionless on a couch and then threatened the boy's brother into repeating a rehearsed story to authorities, prosecutors allege in an affidavit filed Tuesday.

Rex and Rebecca Clark were serving as foster parents to the brothers when Colton Clark disappeared in April 2006. In the affidavit filed by prosecutors, Colton Clark's older brother detailed abuse he said the couple inflicted on the siblings, saying they used broomsticks and extension cords to beat the boys and at times used a red-and-white cattle prod to deliver an electric shock to the boys' genitals. The brother told investigators that around the time Colton disappeared, his aunt and uncle had beaten Colton so badly that the older brother wasn't sure whether his younger brother was breathing.

Rex and Rebecca Clark have not been formally charged in Colton's disappearance, but arrest warrants for the couple filed last week allege first-degree murder, child abuse, child neglect and conspiracy to commit a felony. The prosecutor's office has said Colton is presumed dead, and investigators have been searching the Clarks' property hoping to find his remains. Sheriff's Investigator David Hanson wouldn't say Tuesday whether anything pertinent to the case had been discovered.

The couple appeared in court Tuesday before the affidavit was filed, and Judge George Butner ordered them to return to court next week. Defense lawyer Robert Butler said after the hearing he didn't object to the state holding the pair at this stage.