A former Lehigh University student tried to poison his longtime roommate by slipping deadly chemicals into his food and drink, Northampton County, Pa., authorities announced Thursday.

Yukai Yang, 22, faces attempted murder charges in a case that District Attorney John Morganelli called “weird and bizarre,” saying the roommate once believed he and Yang had a good relationship.

The charges are the latest involving Yang, a student from China who was already accused of scrawling racist graffiti directed at the roommate, Juwan Royal, who is black.

In April, Yang was arrested on accusations of ethnic intimidation after he allegedly wrote the N-word and “GET OUT OF HERE” in marker on Royal’s desk inside their room at Warren Square, and trashed his roommate’s television and bed.

But authorities now believe that in the months leading up to that, Yang, a chemistry major, was putting thallium — an odorless and colorless chemical used as rat poison — into Royal’s food and drink, possibly along with other chemicals, Morganelli said at a news conference.

A motive was unclear, authorities said. Yang and Royal, both seniors at the time, had lived together seemingly without incident for several years.

“Mr. Royal was as dumbfounded by this as anyone else,” said Assistant District Attorney Abraham Kassis, who was involved in the months-long investigation. “He believed they had a fairly cordial relationship as roommates.”

On one occasion in February, authorities said, Royal remembered drinking from a water bottle and feeling a burning sensation on his tongue that left it sore for three to four days.

Twice in March, Royal was so sick that campus police were called to his room, Morganelli said. After one of those calls, Royal was taken to a hospital by ambulance after he reported he had been vomiting for more than 45 minutes, Morganelli said.

Tests eventually revealed that Royal’s blood contained thallium at a level that is dangerous for humans, Morganelli said. Royal’s symptoms matched those of thallium poisoning and included extreme pain in his lower extremities, as well as severe burning and numbness, Morganelli said.

Morganelli said Royal, who graduated from Lehigh last spring, needed intensive medical treatment.

“The victim is still experiencing physical symptoms from the poisoning that occurred, so this is something that has had some lasting impact,” Morganelli said.

Efforts to reach Royal were unsuccessful.

In an interview with investigators on May 25, Yang admitted he used the internet to purchase chemicals that included thallium, and mixed them into food and drinks he stored in a refrigerator he shared with Royal, Morganelli said. But Yang claimed he intended to use the poisons to harm himself “if he did poorly on future exams.”

Those statements contrasted with what Yang told police and Royal at the time of his roommate’s sickening, when he said he suspected “someone” was tampering with items in the room, according to authorities. Yang reported he had noticed the milk in the refrigerator had changed color, as had Royal’s mouthwash, authorities said.

On Thursday, Yang surrendered to Lehigh police to face several charges, including aggravated assault, simple assault, and reckless endangerment. He was sent to the Northampton County prison on $200,000 bail by District Judge Nancy Matos Gonzalez.

Yang’s attorney, Janet Jackson, did not return a phone call seeking comment.

At a court hearing last month in the graffiti case, Jackson identified Royal as her client’s roommate of four years. She said Yang was suspended from school in April because of the vandalism charges, to which she said Yang intends to plead guilty.

But for his arrest, Yang would have graduated in May, Jackson said. She said he has since been living in Easton with his mother.

According to authorities, Yang was identified as the vandal through his handwriting, which mirrored that of the racially charged message.

By then, Royal had begun to suspect that Yang was involved in the “strange incidents” happening in their room, authorities said.