DOVER, Del. (CBS) — Dover police are investigating after a shoplifting suspect died while in custody last month.

Police say 24-year-old John Manning III was taken into custody without incident shortly after 11:30 a.m. on Sept. 20 for a shoplifting incident at a Sam’s Club on North DuPont Highway.

Police say the arresting officer transported Manning to the department’s holding facility until he could be processed and arraigned on the pending charges.

Shortly after 2 p.m., police found Manning unresponsive and not breathing.

Officers immediately performed CPR and notified EMS officials. Manning was then transported to Bayhealth Kent General where he was later pronounced dead.

Manning’s cause of death is unknown as police await the medical examiner’s report.