Doctoral student pleads guilty but mentally ill

Jason Gulley/Exponent Photographer EMOTIONAL PLEA: (LEFT) Zhan Yin, 28, a doctoral student in biology, cried uncontrollably and had to leave the courtroom during his plea agreement hearing Friday to regain composure.

By Laura Pelner
Special Projects Editor

Zhan Yin told the court Friday that he killed a Purdue student last summer because he both feared and hated her and was under the delusion she wanted to hurt him.

Yin, 28, a doctoral student in biology, pleaded guilty to murdering Yeunkyung Woo, 31, a fellow biology doctoral student, and her sister, Hyo Kyung Woo, 29, of Chicago, and he accepted an agreement to plead guilty but mentally ill and receive life in prison without parole instead of the death penalty.

Contrary to the road rage motive he told police in August, Yin said he went to Yeunkyung's Purdue Village apartment Aug. 2 with the intent to harm her.

"I was under the illusion (she and my other lab partners) wanted to hurt myself," he told Judge Donald Johnson.

Yin said he "wanted to kill" Yeunkyung and that he had a hammer with him he intended to use to harm her when he approached her apartment. He said he'd never met Hyo Kyung before that afternoon, but after he knocked on the door and she answered he hit her with the hammer immediately.

He said that after he killed her he realized she was not his target so he moved her body to a bedroom and stayed in the apartment for several hours waiting for Yeunkyung. When Yeunkyung returned home he killed her in a similar manner, with the hammer and a knife.

Before leaving the apartment Yin said he took Yeunkyung's wallet and Hyo Kyung's key chain and he turned on the gas stove's burners.

"I was under the illusion they were still alive," Yin said. "I wanted to turn on the gas to kill them and also to destroy the scene of the crime."

Jason Gulley/Exponent Photographer EMOTIONAL PLEA: Yin's mother held a stuffed animal throughout the hearing and also cried as her son pleaded guilty but mentally ill in the murder of two South Korean sisters last August. The plea agreement would give Yin life in prison without parole in exchange for the death penalty.

As Yin recounted the story he began sobbing. He also cried uncontrollably earlier in the hearing, when county prosecutor Jerry Bean read the charges filed against him. At that point the court took a short recess so Yin could regain composure.

Yin left the courtroom for a few minutes and as he walked out his mother, who held a stuffed animal throughout the hearing, shouted something to him in Chinese; the two started crying.

Yin said he has no history of mental illness and had never been treated for the affliction until recently. Steven Meyer, his lead defense attorney, said experts evaluated Yin for more than 16 hours and found he had several layers of mental illness. However, Yin said he is no longer suffering from the disease.

In addition to two life in prison without parole charges for the sisters' deaths, Yin also has 12 other charges filed against him — two for murder, two for murder while attempting to commit burglary or robbery, two for robbery, two for confinement, two for theft and single ones for burglary and attempted arson.

The court did not yet accept the plea agreement, but Johnson said he would take it under advisement. He said he would wait for more evidence before making a decision and he waived the state law that requires a judge to make a sentencing decision within 30 days of a hearing.

Meyer estimated he'd have more information in June so a preliminary sentencing date was set for 8 a.m. June 28.

Yin, who is a Chinese national, said he has no prior criminal record. He said he received a bachelor of medicine degree, which is similar to a professional degree, from a Chinese university and that he had an internship at a Chinese hospital where he rotated between the surgery and internal medicine units. Before coming to Purdue, Yin studied molecular medicine at Wayne State University in Michigan.

At Purdue he was studying neurobiology, as was Yeunkyung, and both students had the same major professor.

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