(CNN) -- A man pleaded guilty Monday to killing a Virginia Tech graduate student at a restaurant in January, attacking her with a knife and decapitating her, according to officials.
Haiyang Zhu, 26, pleaded guilty to first-degree murder in connection with the death of Xin Yang, a graduate student studying accounting at Virginia Tech, officials said.
Xin, 22, from Beijing, China, had begun her studies at Virginia Tech only two weeks before she was killed at the Au Bon Pain restaurant in the university's Graduate Life Center on January 21, school officials said.
School spokesman Larry Hincker told CNN in January the two were believed to have known each other, based on emergency contact records maintained by the university, but witnesses saw no sign of an argument before Xin was attacked.
Haiyang, a native of Ningbo, China, was taken into custody at the scene.
He had written a love letter to Xin, but she told him she was engaged to another man, Montgomery County commonwealth's attorney Bradley Finch told CNN.
Haiyang purchased the knife used to kill Xin the morning of her death and attempted to call her 12 times, with the first call coming just after he bought the knife, Finch said.
"He completely severed her head," Finch said. Xin also had severe knife wounds to her hands and arms, he said.
In a writing titled "Will," Haiyang said he had expressed love for Xin and that she broke his heart when she said she was engaged to someone else, Finch said. Haiyang said the rejection was too cruel and that Xin's fiance could not compare to him in education and background, and she should have seen he would be the best husband for her.
Haiyang was a graduate student pursuing a doctorate in agricultural and applied economics. Hincker said he began studying at Virginia Tech in the fall of 2008.
Haiyang is scheduled to be sentenced in April, according to court records.
Xin's slaying was the first on the Virginia Tech campus since April 16, 2007, when Seung-Hui Cho killed 32 students and professors before turning a gun on himself.
CNN's Carolina Sanchez contributed to this report.