CUMBERLAND, Md. (AP) — Prosecutors are dropping sexual assault charges against a Frostburg State University police officer in return for his cooperation in a continuing probe of the department.

The charges against 43-year-old Jarrett Warnick were placed on the inactive docket Tuesday in Cumberland. Warnick declined to comment afterward on allegations he forced a female freshman to engage in a sex act in his police car in 2009.

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Prosecutor Gina Cirincion says the charges would have been difficult to prove, partly because the incident allegedly occurred five years ago. But she says Warnick agreed to cooperate in a state police investigation of possible misconduct by at least one other Frostburg State officer.

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Warnick also agreed to resign from the force and not seek another law-enforcement job.

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