What to Know Yukai Yang, a 22-year-old Chinese national, is charged with attempted murder and related charges.

Yang tried to poison his longtime Lehigh University roommate with thallium, once used a household rodent, the DA says.

Investigators said the victim was initially "dumbfounded" by the alleged attacks.

A former Lehigh University student is accused of trying to poison his longtime roommate to death and vandalizing the victim's possessions with racist graffiti, Northampton County District Attorney John Morganelli announced Thursday morning.

Yukai Yang, a 22-year-old Chinese national, is charged with attempted murder and related charges, Morganelli said. He was earlier charged with ethnic intimidation.

Investigators first zeroed in on the suspect after his roommate, who is African American, reported earlier this year that his belongings had been vandalized and scrawled with the N-word, Morganelli said.

Yang was living in the U.S. on a student visa, which has since been revoked, officials said.

As police continued to investigate, they noticed the victim, a senior at the time, appeared to be sick. The victim told police that he had been ill for some time and contacted law enforcement officials in March after uncontrollably vomiting. During that time, police officers were called to his room on multiple occasions and found a racially-charged note on the victim's desk.

The victim told investigators he remembered drinking from a bottle and his tongue starting to burn, officials said.

Blood tests later revealed an increased level of thallium, which was once used as a household rodent or ant killer but has since been banned in the United States, in the victim's blood.

Yang told investigators he saw the victim's milk and mouthwash change color and that he believed someone was tampering with items in the room, Morganelli said.

Yang, a chemistry student, admitted to buying thallium online with the purpose of poisoning himself if his grades went down, Morganelli said.

"This was over a period of time with ... thallium being added to foods and drinks in the refrigerator," Morganelli said. "He was getting worse all the time."

Investigators said the victim was initially "dumbfounded" by the attacks as the two had been roommates for several years and always appeared to get along.

Thallium exposure can lead to nausea, painful limbs, rapid heart rate, high blood pressure, kidney damage and nerve damage, the Centers for Disease Control and Prevention says.

The victim, who has since graduated, is still suffering from ill effects of the thallium poisoning.

Yang was jailed as he awaited a court hearing on the new attempted murder charges. Yang's attorney could not immediately be reached for comment.

This story will be updated to reflect the latest developments.