you see him equally responsible, as michelle gaiser? >> yes. ieve that the evidence shows that he is guilty of solicitation of capital murder. >> reporter: but in a shocking twist, prosecutors revealed they just learned gaiser may have been involved in a previous murder-for-hire scheme and other criminal activity. a likely blow to their case. >> this is a startling revelation. and it severely damages the prosecution's case. their case relies on the believability of the gaiser woman. >> reporter: one person who is not surprised is yvonne, who is steadfast that her husband has flaws. but being a killer isn't one of them. >> the affair, okay. i'll give you that one. but to plot my murder? it's preposterous. >> people have been fascinated about whether -- what yvonne stern did in this situation, is something they could do. but that's not what this case is about. the story of michelle gaiser will make or break this prosecution. and, robin, sources close to this investigation say, that prosecution is in trouble. >> all right, chris. always good to hav

michelle gaiser being implicated in a separate murder-for-hire case.ome out later? >> it's going to leave us and the jury with a lot of second-guessing. if it's true she was involved in another murder-for-hire plot long before evonne stern, is it one of those psychologically off fatal atrarkz mistresses or is this something that jeffrey, her boss, her boyfriend discovered and hatched a plan to get rid of her by using her as a helpless pawn. >> does sh boil down to a classic "he said/she said" in court? >> it does. what we're lacking is direct evidence. even evonne said if you don't have a tape or i'ms or video or adiÓs proving that my husband got michelle to do this, i'm not going to believe it. possibly the jury will think the same way. but all we have is michelle's word against jeff that he's the master mind behind the plot. of course, the question is why would she cop up to 25 years in jail to turn evidence against him unless that was true. she should plead not guilty and take her chances if that's not true. >> let's talk about evonne stern because

. >> she survived being shot but her husband, jeffrey tern and his mistress michelle gaiser were bothfectly clear, jeff stern is innocent of these charges. he had absolutely nothing to do with the vicious plot to kill yvonne. >> and 39-year-old gaiser was expected to testify she was just a go between for jeffrey stern and that he was the mastermind. now as stern was about to go on trial, documents turned over by the prosecution suggest gaiser may have been involved in another murder for hire plot. >> i can't comment on the specifics. but it's our duty to do a thorough investigation to try to reveal the truth. >> her attorneys deny the accusations saying if they had any merit or validity, charges would have been filed. jeffrey stern denies plotting to murder his wife but says he did have an affair with gaiser. yvonne stern filed for divorce and reconciled with her husband and now says she doesn't believe he was involved in trying to kill her. >> she was really willing to forgive jeffrey and to move on because her children and herself she wantsed her family to stay together. >> in excha