(EVANSTON) Northwestern University officials are investigating reports that multiple students may have been drugged and sexually assaulted at a fraternity house last month in north suburban Evanston.

The university’s Sexual Harassment Prevention Office received a report Thursday that four female students “were possibly given a date-rape drug” while attending an event at the Sigma Alpha Epsilon fraternity house in Evanston on Jan. 21, according to a security alert on the university’s website. Two of the students believe they were sexually assaulted.

Another student reported that she was sexually assaulted, possibly with the use of a date-rape drug, at another fraternity house on Thursday, the university said. It was not immediately clear where that incident occurred.

The Sexual Harassment Prevention Office is investigating the incidents, according to the university. Anyone with information about them is asked to contact the university’s Title IX coordinator at [email protected] or call university police at (847) 491-3456.