The body of suspected murderer Daniel Robbins was found in a ditch in a remote forest in Alabama ... and his alleged victim's corpse was lying right beside him.

Robbins allegedly strangled a woman -- Jessica Folds -- to death ... and authorities found him dead on June 10 ... his body was in the fetal position next to Jessica's body.

Investigators believe Robbins had a heart attack while disposing of Folds' body.

Authorities are under the impression Folds was murdered during a domestic dispute ... but no word where the alleged strangulation took place.

Police were called to the scene when a passerby noticed Robbins' pickup truck was still running, with the driver's side door open, parked on a dirt road near County Road 86.

Cops recovered the bodies and turned them over to the Alabama Department of Forensic Sciences for autopsies.