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The district attorney's office reviewed the case Tuesday but then sent it back to Moraga police for further investigation, Priebe said.
Deputy District Attorney Dara Cashman said she would review the case again when tests came back from the county crime lab.
The alleged rape happened Jan. 24 on the school's campus at 1928 St. Mary's Road in Moraga.
The victim identified her assailant as 20-year-old Blake Johnson and police arrested him Friday on a $100,000 warrant.
Johnson has since posted bail and is no longer in custody, Priebe said.
Priebe said police are continuing to investigate the case.
Scott Kier, dean of students at Saint Mary's College, said that, for privacy purposes, he could not say whether Johnson was allowed back on campus. He did, however, say that the college had taken "some interim actions" and would be handling the case in the manner described in the student handbook.
According to the handbook, students are entitled to disciplinary hearings, but in cases that, among other things, involve the safety of students, the school can impose an interim suspension on a student before disciplinary hearings have been held.
Students were sent an e-mail Sunday notifying them of the alleged rape and reminding them of the resources available to them on campus.
According to the e-mail, the rape happened in an on-campus residence.
The school is planning to hold meetings this weekend to remind students of the things they can do to keep themselves safe, Kier said.
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