Cal State University San Marcos is investigating reports by four female students who say they were raped in campus housing since the fall semester began in late August, school officials said Monday.

Each woman reported being assaulted by a different person, and each said she was familiar with her alleged attacker, according to Jerry McCormick, a campus spokesperson. The alleged incidents were not witnessed by other students, he said.

“We are taking what these women say seriously, and the University Police Department is investigating,” McCormick told the Union-Tribune. “UPD is increasing its patrols, and our security escort service will be available to any member of the campus who requests it.”

He said the first reported rape occurred on Sept. 5 at The Quad Residence Hall. The second was alleged to have happened on Sept. 6 at University Village Apartments, which is across the street from campus. The third was reported to have happened on Sept. 13 at Black Oak Hall, a new dorm that opened last month, and the fourth on Sept. 18 at the Quad.

“Sexual assault is never acceptable and is never the survivor’s fault,” CSUSM said in a statement. “Consent must be affirmative, voluntary and ongoing. It cannot be assumed because people know one another or have an existing relationship, and a person who is incapacitated cannot consent.”

The risk of sexual assault for college students is highest at the beginning of the fall semester, especially among freshmen, a phenomenon known as the “red zone.”

“While sexual violence occurs across every academic year, 1 in 6 freshman women experiences sexual assault in their first year of college,” according to RAINN, a national anti-sexual violence organization and operator of the National Sexual Assault Hotline.

A CSUSM student posted a petition on Change.org about the reported assaults requesting that CSUSM “provide more campus security in parking lots, the quad, and other poorly-lit areas on campus.”

“There should also be complete transparency regarding the actions CSUSM will take to actively address this issue,” the petition asks.

More than 400 people had signed the document by late Monday.