The unit is headed by Robert Roeder, a world-renowned scientist working on DNA. 'We have a suspect in mind but proving it is another matter,' said Mr Hill, who described the work at the 15th- floor laboratory as 'highly, highly sensitive'.
The first incident occurred on 6 June when up to 15 people fell ill after taking sugar in coffee and tea. It was thought that spoiled food was responsible, but Mr Hill said that sodium fluoride was the cause. This chemical is used in small quantities in water but is toxic in larger doses. The next day gas jets used as laboratory burners were left on. They could have caused a serious fire. Three days later two threatening letters aimed at two senior women researchers were found in the women's toilets, and two similar letters were sent to university administrators and to Dr Roeder. Mr Hill would not disclose the contents but said that the tone was reminiscent of a crime novel.
Police do not believe the suspect has murder in mind. 'I believe that if that person wanted to kill somebody, he would have killed them,' Mr Hill said. He added that the police and university had tried to minimise publicity, but reversed that policy after a report appeared in the Wall Street Journal. The newspaper quoted unidentified staff as saying there were severe tensions among the researchers.