Police said they found "several documents" at the scene that led them to believe Jennings killed Allison Castro and disposed of her body.
Castro was reported missing on Sept. 19 after her family was unable to contact her, KNWA/KFTA-TV reports. Jennings and Castro were allegedly previously in a relationship and lived together.
Jennings was arrested after his release from a local medical facility on Sept. 26 and charged with capital murder and abuse of a corpse, according to police.
Sgt. Tony Murphy with the Fayetteville Police Department told KNWA/KFTA, "Some of the information that’s been located during the investigation led us to believe that the body of Castro was moved, or was disposed of, so that’s the basis of the abuse of a corpse charge."
The Benton County Sheriff’s Office is assisting the Fayetteville Police Department with the search for Castro’s body, KNWA/KFTA-TV reports. Officers reportedly have evidence suggesting the body is near Beaver Lake in Arkansas.