PHILADELPHIA, June 18 (UPI) -- Police said a human skull was found inside an apartment that had recently been vacated by a group of seven University of Pennsylvania students.

Philadelphia police said an assistant manager of the apartment building found the skull on the kitchen counter after the students had left, WCAU-TV, Philadelphia, reported Wednesday.

Investigators said they do not know which of the students left the skull behind and thus far there is no indication that a crime has been committed.

Lt. Frank Vanore said the discovery makes "kind of a weird story," even for the Philadelphia police. He said the skull may have been used as a learning tool for a medical student or it may have been purposefully left in the kitchen as a prank.

Jeff Moran, a spokesman for the Philadelphia Medical Examiner's Office, said the skull will be analyzed by a forensic anthropologist.