The student who killed 32 people at Virginia Tech before committing suicide had no prescription drugs or toxic substances in his system, state police said Thursday.

The toxicology tests, performed as part of Seung-Hui Cho's autopsy, answered one of the key remaining questions in the investigation of the gunman who opened fire April 16 in a dormitory and a classroom building.

Cho, 23, shot himself as officers closed in. His autopsy report confirmed that he died from a self-inflicted gunshot wound to the head, police said.

State police said they will not release the complete autopsy reports on Cho or his victims because the criminal investigation is ongoing.

A state panel investigating the shootings is reviewing Cho's contact with the mental health system. Cho was ordered into involuntary outpatient treatment in 2005 after a judge found that he was a threat to himself. But there is no indication he ever received treatment.

In other developments, the university is rolling out plans for an expanded emergency notification system that will allow students, faculty and staff to be alerted to emergencies by text messages, e-mails and online instant messages.

Starting July 2, members of the Tech community can sign up for the expanded "VT Alerts" system, which will be ready when classes resume Aug. 20.

Virginia Tech began considering expanding its emergency alert system well before the shootings, university spokesman Larry Hincker said.

Plans to revamp the system began last fall after an escaped prisoner accused of killing a hospital security guard fled to the university area and caused the campus to shut down.

The school was in the process of selecting a vendor for the new alert system when the shooting spree occurred.

"We were already rolling down this path before April 16th came along," Hincker said.

The new technology is being provided by a company called 3n (National Notification Network), a California-based provider of mass notification systems. Students and staffers will be able to receive alerts by cell phone text message, online instant messages, phone calls and e-mails.

Students and staffers eventually will be able to add phone numbers, e-mail addresses and instant-message screen names for their friends and family members to the system, too.

During the shootings, the university relied mainly on e-mails, the campus siren and a message on the school's Web site to alert students to the danger, Hincker said. At the height of the crisis, the Web site received 150,000 hits an hour, he said.

Since then, the school has been conducting a sweeping review of campus safety. Dorms will now be locked 24 hours a day, accessible only by swipe cards. School officials are debating whether to add locks to classroom doors. And the doors at Norris Hall, which Cho chained together before killing 30 people inside, have been modified so they can't be rigged shut.