PRESQUE ISLE – The State Medical Examiner’s Office has determined the cause of death in a car accident last month that killed three adults and injured two others near the Presque Isle-Easton town line.

Mitchell Cyr, 22, and siblings Libby Hill, 21, and Michael Hill, 24, of Presque Isle died in the single-car accident on the Cleaves Road.

Libby and Michael Hill died of blunt head injuries and Cyr died of blunt injuries, an official with the State Medical Examiner’s Office said Wednesday.

The Presque Isle Police Department has closed its investigation into the crash, Detective Wayne Selfridge of the department said Wednesday.

Alcohol and speed were determined to be contributing factors in the fatal accident, he said.

Two men, Andrew Ladner, 21, a University of Maine at Presque Isle employee, and Travis Bryant, 21, an UMPI student and Newburgh resident, survived the accident. Ladner was treated for head injuries at Eastern Maine Medical Center in Bangor. Selfridge said Ladner has been transferred to a head trauma center in the Bangor area.

“He’s not too medically responsive yet to any questions,” the detective said.

Bryant was released days after the accident from The Aroostook Medical Center in Presque Isle after he was treated for cuts, abrasions and a seat belt bruise.

Presque Isle Police Chief Naldo Gagnon said recently that there were no witnesses to the accident.

Police believe the vehicle, owned by Libby Hill, went off the road, down into a ditch, and struck a large rock and tree. The car then rolled over and caught on fire when it came to rest, the chief said.

The victims were burned badly in the accident because they were too close to the car after it caught fire, the chief said. The other two passengers were ejected “very far away” from the burning car, he said.

Police questioned Bryant during their investigation, but said he was unable to remember the details of the accident.

Selfridge said Bryant doesn’t recall who was driving that night and that because the case has been closed, the driver will not be determined.