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LAFAYETTE, Ind. (AP) _ A Purdue University doctoral student has agreed to spend the rest of his life in prison for killing two South Korean sisters in a campus apartment last year.

Zhan Yin, 27, of China pleaded guilty but mentally ill to two counts of murder and other charges Friday. He could have faced the death penalty if he had been found guilty at trial.

A judge took the plea agreement under advisement. A sentencing hearing was set for June 28.

Yin admitted to killing Yeunkyung Woo, 31, and Hyo Kyung Woo, 29, last August.

Yin allegedly told investigators he followed Hyo Kyung Woo to her sister's apartment and killed her after a car she was driving nearly struck him while he was bicycling on the West Lafayette campus.

He was arrested four days after the killings after he was refused entry into Canada at a border crossing near Niagara Falls, N.Y.