there was no solid evidence earring either way, nor than james matlean killed ben oxley, only dawn'snt the assistant district attorney tom gregory decided he needed her help. >> you love to get everybody involved in the case, but there's a reality in many cases that sometimes you need the help of one of the people involved to get the main person. >> and so dawn oxley was offered a limited immunity agreement, cooperate with the prosecution, testify truthfully against james matlean, and you won't be prosecuted. a sort of get out of jail free card. why go ahead and make that deal with her so soon? you had her statement. why not hold off for a while and be patient and then get them both? >> let's say we don't do the deal with her and we go out and arrest him. what's our evidence? >> dawn signed the agreement and james was charged with first-degree murder. but the end of the story, oh, no, not even close. the truth had been hiding but it was itching to come out. young devin, remember him? dawn's son? devin finally decided it was time to reveal what he overheard the night of the murder. >>