Blacksburg, Va. ? Virginia Tech gunman Seung-Hui Cho was as mysterious in death as he was in life, leaving behind few clues for medical examiners.

Dr. William Massello, the assistant state medical examiner based in Roanoke, said Sunday that Cho died from a self-inflicted gunshot wound to his temple after firing enough shots to wound his 32 victims more than 100 times.

But there was nothing unusual about Cho’s autopsy, he said, and nothing that would have hinted at any psychological problems that might have led him to commit the worst shooting massacre in modern U.S. history.

Pathologists sent blood samples for toxicology testing to determine if Cho was on drugs at the time of his rampage, but Massello said it could take as long as two weeks to get results.

Police are still searching for a motive. Cho, the 23-year-old English major who was described as reclusive and extremely shy, left behind a package of videos and letters railing against privilege and wealth but did not say how he chose his victims.

Those victims apparently did not fight back against Cho’s ambush. Massello said he did not recall any injuries suggesting a struggle. Many victims had defensive wounds, indicating they tried to shield themselves from Cho’s gunfire, he said.

Massello said Cho hit many of his victims several times.

Authorities had to return to the victims’ dorm rooms and homes to collect fingerprints so they could make identifications, according to an official close to the investigation who spoke on condition of anonymity because the probe is ongoing.

Several of the victims had gunshot wounds to the head, the official said.

Many of the victims’ bodies left the medical examiner’s office on Thursday, the official said, adding that several major airlines offered to transport the remains back to their families for free. The official was not sure if Cho’s body was among those that had been released.