WASHINGTON — Things finally seemed to be going better for Noor Salman and her husband, Omar Mateen. He had been accepted into a police training program and had showered her with jewelry to celebrate. He had given her permission to visit her family in California and handed her spending money for the trip. And he had stopped hitting her.

So when Mr. Mateen told her that he would not be home for dinner the afternoon of June 11, she asked him not to go. It was Saturday — and she hoped it would be a family night. But he told her that he had to see a friend, kissing her and hugging their 3-year-old son as he left.

Mr. Mateen never returned home. Instead, he drove two hours from the family’s home in Fort Pierce, Fla., to a nightclub in Orlando, where he killed 49 people and wounded dozens more before the police fatally shot him, ending one of the worst terrorist attacks in the United States since 2001.

Ms. Salman, whose parents immigrated to the United States from the West Bank in 1985, was immediately a person of interest. F.B.I. agents questioned her for hours, eliciting from her that she had been with her husband when he bought ammunition and scouted the club. Some agents came to believe that she was not being truthful.