The Federal Bureau of Investigations in Louisville has released the immediate cause of 23-year-old Mariah Amber Decru's death.

Decru's body was found within Zion Hill Cemetery at Mammoth Cave National Park in March.

“The immediate cause of death was 'acute diphenyhdramine intoxication' and the manner of death was listed as 'undetermined.' No foul play is suspected,” said Detective Timothy Beam with the FBI in Louisville in an email to the Glasgow Daily Times on Friday afternoon.

A person found Decru's body at the cemetery and then reported the discovery to Barren County dispatch.

The Park City Volunteer Fire Department notified park rangers with the national park about Decru's body being found.

The National Park Service and the FBI then began investigating the incident.

A press release from the national park issued in March said the cause of death could not be confirmed at that time and that investigators were awaiting a report from the medical examiner's office, plus various tests before information about the cause of death could be released.