LINCOLN, Neb. (AP) -University of Nebraska police are looking for a man who left two threatening voicemail messages for Cornhuskers defensive coordinator Kevin Cosgrove.

According to court documents obtained Wednesday, one expletive-laced message suggested Cosgrove go back ``where you came from you ... before I ... kill ya.''

The messages were left between midnight and 3 a.m. on Nov. 4. Cosgrove told police he was concerned for his safety after hearing the messages. Cosgrove, through sports information director Keith Mann, declined to comment Wednesday.

Windstream Communications, the university's phone carrier, turned over to police a record of incoming calls to the football office's general number and to Cosgrove's extension. Those records didn't lead to the source of the calls, Capt. Charlotte Evans said. She said police were investigating another lead.

John Backer, the investigator handling the case, referred questions to university police chief Owen Yardley, who was out of the office.

Cosgrove has been a frequent target of fan criticism this season. The Huskers' defense statistically is one of the worst in major-college football.

Cosgrove received ``numerous'' phone messages containing vulgar language in past weeks, according to court documents.

The message that prompted him to contact police was left on his voicemail hours after Nebraska's 76-39 loss at Kansas.

An administrative assistant in the football office contacted police on behalf of Cosgrove. She said on the first message the caller ``used vulgar language to express his negative opinion of Kevin Cosgrove's performance as a coach,'' a court document said.

The second message immediately followed. In that message, the man called Cosgrove an expletive and said, ``You got 76 points scored on you.''

Evans said this is the first time this season campus police have been called about possible threats against a member of the football coaching staff.

``It's not typical for this to happen,'' Evans said.