BERLIN (AP) — Investigators said Thursday they have identified a 32-year-old student as the suspect in the poisoning of seven people at a university in western Germany last year.

In August, prosecutors opened an investigation after employees and students at the Technical University in Darmstadt, south of Frankfurt, received medical treatment for symptoms of possible poisoning. Police said at the time that milk cartons and water containers in a building on the campus appeared to have been contaminated.

On Thursday, they said the 32-year-old from the German city of Mainz, a materials science student at the university since 2017, has been sent to a psychiatric hospital. She is suspected of attempted murder, but officials believe she can't be held criminally responsible because of a psychiatric illness. Police said the suspect hasn't yet responded to the allegations.

They said information from over 1,000 witnesses helped firm up their case against the suspect, and that forensic analysis pointed to her having been in the building the night before the victims' symptoms appeared.

Some of the affected employees were mentioned in notes written by the woman, and the investigation found indications that she felt persecuted by them, police said. They didn't identify the “harmful substances” that were used.