Killed were Capt. Philip Esposito and 1st Lt. Louis Allen, both National Guard officers in the 42nd Infantry Division. Martinez is charged with two counts of premeditated murder. He could be sentenced to death if convicted.
Martinez has pleaded not guilty. Defense attorneys say Army investigators have no evidence and targeted Martinez because he was feuding with Capt. Philip Esposito.
The case is expected to last through the end of the year.
Siobhan Esposito and Barbara Allen testified briefly Thursday to identify their husbands for the record.
Esposito identified a photo of her husband that he had e-mailed from Iraq. The photo was displayed on two television screens in the courtroom. She said she last saw her husband on New Year's weekend, 2005, when she drove to Fort Drum, N.Y., to visit him.
Defense attorneys asked if she had ever heard of Martinez.
"My husband never talked about his work while he was in Iraq," she responded.
Defense attorneys objected when prosecutors asked if Martinez had ever had contact with her. Out of the jury presence, when asked if he had ever done or said anything to her, she responded, "I believe that he murdered my husband. I've been here for every hearing and I am firmly convinced that he murdered my husband."
She also said that occasionally he made eye contact with her in the courtroom in previous hearings and she felt he was looking at her with contempt. The judge sustained the defense objection and the jury was not allowed to hear the testimony.
Barbara Allen testified the last time she saw her husband was Memorial Day 2005. She said after he got to Iraq, he set up a Web cam so they could talk and see each other every day, along with their children.
"About 10 hours before he died, we did a video chat," she said.
Esposito, 30, of Suffern, N.Y., worked as an information technology manager in Manhattan and was Martinez's company commander. Allen, 34, of Milford, Pa., was a high school science teacher and the company operations officer. The Espositos had a young daughter, and the Allens had four young sons.