A preliminary autopsy shows the attacker at Ohio State University died from gunshots to the head and chest.
A campus police officer shot the Somali-born student within a minute of his car-and-knife attack that left 11 hurt on Monday morning.
The coroner's office in Columbus said Wednesday that it could take eight more weeks before it can issue a final report on the death of Ohio State student Abdul Razak Ali Artan.
Investigators said Wednesday that the 18-year-old bought a knife on the morning of the rampage, but it's not clear if that's the weapon he used.
The FBI also says the investigation has not found that anyone else was involved in the attack or the planning of it.
Authorities are looking into whether the attack is linked to terrorism.
