Our year-long hidden camera investigation into the state-run Rainier School for the Disabled has already revealed terrifying physical abuses and an orchestrated cover-up regarding a client's death.

Now, KIRO Team 7 Investigative Reporter Chris Halsne discovers yet another fatal accident; this one involving a psychotropic drug.

50-year-old Kent Zimbelman had been institutionalized inside the Rainer School for the Disabled since he was nine. He suddenly died July 22nd.

A KIRO Team 7 Investigation found medical staff gave Zimbelman a fatal dose of the wrong medication.

KIRO Team 7 Investigators have shown you Rainier School employees who punch and shake severely disabled clients.

We've also let you hear some of the abuses that have been kept secret inside these brick walls for years, like employees punishing patients by rolling up patients in mats, giving them cold showers, or suffocating them.

Now, KIRO Team 7 Investigators lay out a roadmap of how understaffing inside the Medical Ward at Rainier might have played in role in killing a helpless man.

Kent Zimbleman had epilepsy. It's commonly known that patients with that disorder are not supposed to have a schizophrenia preventative called clozapine. Its main side effects are seizures and convulsions.

Pierce County Medical Examiner Eric Kiesel confirms a nurse handed Zimbelman clozapine, even though nobody had ever prescribed it to him.

"It's in his system and it's not supposed to be in his system. We know it aggravates seizure disorders because that is how we determined the cause of his death."

An autopsy confirmed the drug triggered severe seizures, killing Zimbelman.

The fatal mistake may not have been caught if it weren’t for our repeated investigations into abuses at Rainier over the past two years. Because of our work, the medical examiner decided to start reviewing every death that occurred at the facility.

Kiesel told us, “We've been looking at cases coming out of Rainier School. It's a state institution and we've just been monitoring it. It was brought to our attention a while back that there were some concerns out there. Basically, we investigate all deaths that occur at Rainier School, and the good news is that we really haven't been finding problems. This is the first one in a long time that there was actually a problem.”

KIRO Team 7 Investigators discovered: Zimbelman’s medicine mix-up is just one of dozens at Rainier recently.

Documents from the Department of Social and Health Services, which runs Rainier School, show 26 medication mistakes in the 6 months prior to Zimbelman's death. That’s 26 errors from June to December of 2007 that led to a variety of unnecessary injuries.

We even found another clozapine error in that short time frame.

Records show that an "LPN did not follow the facility's procedure which was developed in order to prevent medication errors involving the drug Clozaril (the namebrand of clozapine) . The LPN gave Individual #1 the medication meant for Individual #2. (Person) became unresponsive and a Code Red."

Director of the Rainier School for the Disabled, Neal Crowley, apparently knew he had potential problems with mixed-up meds the month before Mr. Zimbelman's death.

We obtained this internal memo he sent out to staff in May.

"We have been unable to fill 35% of our LPN positions. At times we have not had enough nurses to pass medications without increased risk of medication errors. - Our nurses are getting tired, working much overtime, and being continually asked to do more and more."

Detectives from the Washington State Patrol are currently conducting a criminal investigation into Zimbelman's death.

In theory, the Medical Licensure Board decides if the nurse, who made the medicine mistake, violated professional standards. However, that agency didn’t know about the death until we told them.

DSHS and Rainier School Administrators declined to speak on the record about this case.

Zimbelman's family declined comment as well.