The authorities closed off the affected building and took away food that had been on-site for further investigation. They recommended that anyone who shows possible symptoms or whose "extremities turn blueish" seek immediate medical assistance.
What are the police doing?
Authorities have launched a 40-person murder commission under the name "Licht" (the German word for "light"). Further personnel would be added if needed, the statement said.
"The investigations are currently in full swing and the police are doing everything to detect the culprit as soon as possible," the Hesse police said.
The first symptoms appeared on Monday during the day. No other individuals have reported symptoms since then. Police searched other buildings on the campus but found no further traces of the substance.
The police said the situation no longer posed an acute threat.
How did the university respond?
"We are shocked by the apparent offense that happened at our university," the university's president Tanja Bruehl said in a statement.
"I wish the affected all the best, a quick recovery and can assure them my full support," Hesse's science minister, Angela Dorn, said. "Together with the university and investigators, we now need to clarify the situation as quickly as possible."
A statement on the university's website recommended that staff and students, for the next few days, avoid consuming or preparing food that has been stored on the university campus.