The autopsy report for the University of Kentucky cheerleader Laken Snelling‘s infant has been completed … but investigators are still left with questions about how the baby died.

A report from the Fayette County Coroner’s office obtained by TMZ reveals the cause of death of the baby boy — who died on August 27 — is inconclusive and that “extensive microscopic analyses are essential to determine the cause and manner of death.”

Coroner Gary W. Ginn confirms the investigation remains open and his office is “conducting a thorough and methodical death investigation to ensure all facts are carefully considered.”

As we reported … an infant boy was found dead and wrapped in a towel in a trash bag located in a closet last week … and the 21-year-old stunt performer was arrested Sunday.

Snelling was subsequently charged with abuse of a corpse, tampering with evidence and concealing the birth of an infant.

Law enforcement sources tell TMZ she has admitted to the crime.