Courtroom cameras have been turned off during the testimony of Detective Adam Dismukes to protect his identity.
Dismukes said a friend of Nancy Cooper told him items in the Cooper's Cary home were missing or moved around.
When asked by Brad Cooper's attorney what that indicated to him, Dismukes said: "Possibly that a struggle ensued there."
Brad Cooper is charged with first-degree murder in the death of Nancy, whose partially clothed body was found by a man walking his dog in an undeveloped subdivision not far from her home on July 14, 2008 - two days after she was reported missing. She had been strangled. Prosecutors say Brad killed her because he was angry she intended to leave him, take their children, and move to be with her family in Canada.
Nancy was last seen alive by friends at a party on the evening of July 11.
Asked what he concluded from the evidence he gathered and other things he saw at the house, Dismukes said: "I believe Nancy Cooper came home from the party on July eleventh, or the early morning hours of July twelfth and Mr. Cooper murdered her."
He also testified that items in the Cooper's garage were pushed to one side. Dismukes said witnesses told him the Coopers normally had so much stuff in their garage that you couldn't pull a car inside. He said it appeared Cooper made room to pull a car in so he could load the body.
But Dismukes couldn't identify which car or exactly when - only that it was likely in the 12 hours or so between when Nancy came home and the time that one of her friends reported her missing the following afternoon.
Cooper's defense attorneys have said that Nancy's friends convinced police that Brad was guilty and investigators ignored any evidence that didn't fit that scenario. They've suggested someone else was the killer.
On the stand Thursday, Dismukes testified that another investigator pointed out to him that Brad Cooper had red marks on his neck the day Nancy went missing. When asked if, when taking almost 100 pictures that day, if he asked Cooper for permission to photograph his neck or took any without him knowing, the answer was "no."
The prosecution has yet to present any physical evidence linking Cooper to the crime. Several former friends and neighbors have testified that he had affairs and that the marriage was deeply troubled. They also said Cooper was acting strangely the day Nancy was reported missing.
The defense has a continuing objection to witnesses testifying about what Nancy Cooper told them since the defense cannot cross-examine Nancy Cooper. Superior Court Judge Paul Gessner has repeatedly denied those objections. He has told members of the jury that they can only use such testimony to establish Nancy's state of mind.
Defense attorney Howard Kurtz acknowledged that Brad Cooper had an affair in his opening statement, but also said Nancy was involved in a relationship with another man. He even raised questions about the paternity of her youngest daughter, who was born eight months and 24 days after Kurtz said Nancy and the man had an encounter.
The Coopers relocated to Cary from Canada in 2001 when Brad Cooper took a job at Cisco Systems in Morrisville. He studied computer science at the University of Calgary and took graduate business courses at North Carolina State University.
Nancy Cooper's parents now have custody of the couple's two children in Canada.