Magalie Lelong took the stand for the prosecution on Wednesday. Prosecutors allege that Campbell had an intimate relationship with her before Heather Domenie's death.
LeLong said she talked to Campbell just before he called 911.
"He said that when he got back from the grocery store, he found Heather dead in the bed," she said.
The prosecution alleged Domenie found out that Campbell and Lelong had spent the night together at their home the night before her death.
Jurors saw more forensic evidence Wednesday during the trial, including pictures of the master bedroom where Campbell told investigators Domenie was for most of the day. Tom Como, an investigator with the city-county bureau of identification, showed jurors a bucket from the bedroom that contained wine glasses, a piece of bread and evidence which suggested that someone was sick.
After authorities removed Domenie's body from the crime scene, Como said he returned to the crime scene to take pictures. Como told jurors that Campbell was present when he was taking pictures.
"He was following me around pretty closely, especially when I was upstairs photographs and collecting items of evidence," he said.
Jurors also saw a torn tea towel that contained hair and fibers from Domenie. Authorities say Domenie, a Raleigh school teacher, was strangled to death.
Campbell acknowledged responsibility for Domenie's death, but he alleges that he did not mean to kill her. The state is seeking the death penalty in the case.
Campbell is expected to take the stand in his own defense on Friday.