Georgetown University’s campus police chief confirmed Wednesday that emergency officials discovered ricin in a student’s room this week.

The substance was found in McCarthy Hall on Tuesday morning and tested positive for ricin, a poison that is deadly to humans.

Georgetown University police chief Jay Gruber said in an email to students that tests of the room later in the day yielded no other “biological threat agents” and the room was cleaned by contractors trained in removing toxins, Gruber said. Students have now been allowed to return to the dorm.

Gruber said the university received no reports for ricin exposure symptoms, and the 24-hour timeframe when symptoms usually appear has lapsed.

He said Tuesday that a suspect had been found and police were conducting interviews.