A University of California at San Francisco researcher accused of trying to poison a female coworker pleaded not guilty today in San Francisco Superior Court to charges of attempted murder, poisoning and assault with a deadly weapon, his attorney said.
Ben Chun Liu, 38, a Chinese post-doctoral student in the United States on a work visa, was arrested Friday and remained in custody today on a no-bail immigration hold.
Liu allegedly poured a lab chemical into the drinking water of 44-year-old lab technician Mei Cao on two occasions in recent weeks, according to university police.
The first incident occurred Oct. 23, police said.
The chemical was identified as ethidium bromide, according to court documents filed today by prosecutors.
Ethidium bromide is used commonly in laboratories and, according to federal safety guidelines, is considered hazardous if ingested.
However, little is known about its long-term toxic effects on humans.
Following the incidents, Cao was examined at the UCSF Medical Center and later released.
She is in good health now, police said.
Liu's attorney Bill Fazio said today he is still reviewing evidence in the case, but argued that if the chemical is not a poison, his client would be innocent of the charges, even if he had intended to use the chemical to poison someone.
Both Liu and Cao worked at the university's urology department, according to the school.
Police said Cao noticed there was something in the water after drinking some of it, and notified police after Liu allegedly admitted to her that he had tried to poison her.
A motive for the alleged poisoning is still not known.
Liu would only tell police that he had been "stressed out," police said.
According to police, the two had worked together at the lab for at least a year, and did not have a romantic relationship.
Police said Liu had never expressed any hostility toward Cao.
Liu is scheduled to return to court Friday to set a date for his preliminary hearing, Fazio said.