Police think that a serial rapist may be targeting college-age women near the Kansas State University campus, attacking seven women over the last seven years, including one attack last month, according to a report in the Kansas City Star.

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Police say that because the man wears a mask, they do not have composite of the rapist and have few leads to track down, the Star reports.

After the attacks, police have released crime prevention tips to help keep students on the campus of 23,000 safe, including handing out fliers on campus telling female students how to protect themselves, such as walking with a friend and keeping windows and doors locked.

“If someone is able to protect themselves from the opportunist rapist, you can protect yourself against the serial rapist,” said Capt. John Doehling of the Riley County, Kansas, Police Department, which covers Manhattan and the Kansas State campus.

“Yes, we believe there is one guy doing this. But if it was seven different persons committing these crimes over the course of seven years, people would still need to be concerned,” said Doehling.