Raleigh, N.C. — A man who was supposed to play tennis with Brad Cooper the day his wife disappeared says in a new court filing that police tried to "coerce" him into saying he helped establish an alibi for Cooper, now at the center of a custody battle for his two young daughters.

In an interview with police four weeks ago, Michael Hiller states in a Sept. 29 affidavit, investigators used "good-cop bad-cop" tactics to force him to admit he made calls on Nancy Cooper's cell phone on July 12, the day a friend reported her missing.

He also says police told him the Town of Cary was calling her homicide isolated "so people like you would be more comfortable."

Police have said the crime was not random violence.

"The police told me they had to investigate Brad because he was the husband," Hiller states in the document. "They also told me that if they were to arrest someone else without thoroughly investigating Brad, the lawyer for that arrested person would accuse them of doing poor police work."

Cary police had no comment on Hiller's affidavit, a town spokeswoman said.

In a phone interview with WRAL News Thursday morning, Hiller said he backs his statements, but also said he does believe Cary police are doing a good job with the case.

"We are just looking for justice for Nancy and the girls and for Brad, wherever the cards may fall," he said.

A man walking his dog found Nancy Cooper's body on July 14 in an undeveloped subdivision three miles from the Coopers' Lochmere home. An autopsy determined she had been strangled.

Her parents, Garry and Donna Rentz, filed for custody of the couple's children two days later, claiming Brad Cooper is mentally unstable and poses a threat to the children.

Cooper, who declined to comment Thursday, gave a deposition for more than seven hours to the Rentzes' attorneys. They were able to ask him anything that relates to his fitness as a parent, including whether he played a role in his wife's death.

Police have not named a suspect in the case. There has been widespread speculation that Brad Cooper was involved, but his attorneys have repeatedly denied that he killed his wife.

Cooper had to answer the deposition questions or be held in contempt of court. He did have an option, however, to invoke his Fifth Amendment right on any question that might have incriminated him.

"We think we're making progress toward a conclusion," Garry Rentz said. "We can't say anything more than that."

Brad Cooper's attorneys will depose the Rentzes and Nancy Cooper's twin sister, Krista Lister, next week. The temporary custody hearing is scheduled for the week of Oct. 13.

"It has been a long day," the Rentzes' attorney, Alice Stubbs, said Thursday evening. "We're thankful we got through it, and everybody worked hard. We'll be back to work tomorrow."