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.

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

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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.

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