Craig Miglucci was the first of several rebuttal witnesses called by prosecutors after the defense rested its case Friday.
Miglucci said a computer chat between himself and Cooper in 2008 showed Cooper had a computer router in his home that was capable of generating a phone call from Cooper's home to his cell phone.
Cooper is accused of killing his wife Nancy. She was last seen alive by friends at a neighborhood party in her Cary subdivision the evening of July 11, 2008.
Cooper told detectives his wife returned late that night and went out for a run around 7 a.m. the next morning but never returned. Her body was found by a drainage pond in an unfinished subdivision a few miles from her home two days later. The medical examiner said she had been strangled.
While prosecutors claim Cooper killed Nancy after she returned from the party, part of his alibi is that telephone company records show phone calls were made from the Cooper home to his cell phone the morning of July 12.
Cooper told detectives Nancy called him while he was making a run to the grocery store.
The prosecution maintains that Cooper - a telephone expert who worked for Cisco until his arrest - had the knowledge to use his home computer to fake the phone calls.
On the stand Monday, Miglucci said he and Cooper had an online conversation about a computer router capable of making the call and Cooper said he had one at home.
While detectives never found the router in Cooper's home, Miglucci testified one was missing from Cisco inventory.
On cross-examination, the defense raised questions about when the router was received from the manufacturer - suggesting it was received after Cooper was arrested. But Miglucci testified he signed for it when it arrived earlier than that.
The defense rested on day 36 of the Brad Cooper murder trial Friday. Closing arguments are set to begin Tuesday. The trial has become one of the longest not involving the death penalty in Raleigh history.
Presiding judge Paul Gessner ruled Monday that the jury will have the choice of first-degree murder, second-degree murder, or not guilty. The defense objected, saying they wanted just first-degree or not guilty, but Gessner cited legal precedent.
Gessner also said he would limit closing arguments to two hours for each side.
Prosecutors allege Brad killed Nancy because he was angry she planned to divorce him and move with their two daughters to Canada.
Cooper's lawyers say he is innocent and have characterized the investigation by the Cary Police Department as inept. They say detectives focused on Cooper from the beginning of their investigation and never looked at other suspects.