After the brutal murder of his first wife, Mark Winger moved on. After all, he was seen as the hero who tried to save her, subsequently killing her supposed murderer with his handgun moments later.

Police quickly concluded the 1995 killing of Donnah Winger was a tragic incident, committed at the hands of a seemingly mentally unwell driver who’d once driven her home from the airport.

It was an earth-shattering tragedy for Donnah’s family and Winger went on to marry the beautiful young nanny that he’d hired to care for his and his late wife’s recently adopted newborn. He then had three more children with her in the following years.

It wasn’t until 1999, more than three years after Donnah’s murder, when her best friend DeAnn Schultz came forward to say that she’d had an affair with Winger before her friend’s killing that police began to look deeper into the case.

At the time, Schultz told police that Winger had made several incriminating comments, including, “It would be easier for us to be together if Donnah just died,” and, “All you’d have to do is come in and find the body.” Schultz said she felt at the time that the comments were just “crazy talk.”

Donnah’s family and Winger’s ex-wife, Rebecca Simic, spoke to “20/20” about the horrific realization that Mark Winger was a manipulative killer hiding beneath the mask of a brilliant engineer and a kind, loving husband and father.