Authorities have determined that skeletal remains found off a hiking trail in Middle Island on Friday are, in fact, human — but said Monday that the cause of death remains undetermined.

Suffolk County police said a man found the bones near Rocky Point Road at Yaphank Middle Island Road just before 3:30 p.m. and that he immediately called 911.

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Investigators initially said it was unclear if the bones were human or that of an animal.

Additional investigation is being conducted by the Medical Examiner’s Office. No identification has been made.