A former Lehigh University student charged with poisoning his roommate posted $200,000 cash bail and hoped to be deported to China to avoid prosecution, a prosecutor said Thursday. Yukai Yang, 23, was back in local custody after authorities learned of the plan and had him returned from U.S. Immigration and Customs Enforcement (ICE) custody to the Northampton County Jail in Pennsylvania.

Prosecutors are now asking a judge to keep Yang locked up without bail, calling him a "legitimate flight risk."

They are meanwhile investigating whether a second student was also poisoned with the chemical thallium.

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That is in the early stages of investigation. It came to light essentially after the publication of these charges," District Attorney John Morganelli said.

"Mr. Yang thought that because he is a foreign national, now here illegally in that his student visa has been revoked, that he could post bail, waive his right to a deportation hearing and abscond," Morganelli said in a statement. "That will not happen."

He believed that Yang's mother posted the cash bail this past week. Court papers identify the person as Hua Shi. Yang's lawyer did not immediately return a call for comment Thursday.

Yang, a senior chemistry major, was charged Dec. 20 with poisoning his roommate's food, drink and mouthwash with thallium over several months, causing the victim, Juwan Royal, bouts of dizziness and vomiting. Royal was so sickened that on two occasions in March campus police were called to his aid, authorities said.

Investigators think Yang bought the odorless, colorless chemical, once sold as rat poison, online, Morganelli said.

He was initially charged in April with vandalism and ethnic intimidation after Royal, who is black, found racist graffiti in the room. Police said Yang wrote the N-word and "GET OUT OF HERE" in marker on Royal's desk in their room at Warren Square and also trashed Royal's television and bed, the Morning Call reported.

The roommate has since graduated, but continues to suffer effects of the poisoning, authorities said. The two had lived together for several years without incident, authorities said.

Yang is charged with attempted murder, aggravated assault, ethnic intimidation and other charges.

A preliminary hearing is scheduled for next week.