carter. >> and what a deal he made. >> reporter: sebesta had a powerful card to play: carter's wife, teresa. shortly after the killing, sebesta had also indicted her for capital murder. >> she had given conflicting statements about his burns. there were a number of things that she did. >> reporter: the deal sebesta made: he would not question carter about his wife on the stand if he testified against graves. >> how does a prosecutor... i should say, how does an ethical prosecutor put a witness on the stand, your main piece of evidence in a death penalty case, and say, "okay, you get up there and talk about what you did and what graves did, but i'm not going to ask you about your wife." you can't do that. >> reporter: why in the world would you agree not to ask him about her? >> well, i needed his testimony. >> reporter: and sebesta points out the deal was approved by a judge and the defense never questioned it. >> that put on the record, i did put on the record. >> reporter: the indictment against carter's wife was later dismissed due to a lack of evidence. and siegler never bought i

carter. >> and what a deal he made. >> reporter: sebesta had a powerful card to play: carter's wife, teresa. shortly after the killing, sebesta had also indicted her for capital murder. >> she had given conflicting statements about his burns. there were a number of things that she did. >> reporter: the deal sebesta made: he would not question carter about his wife on the stand if he testified against graves. >> how does a prosecutor... i should say, how does an ethical prosecutor put a witness on the stand, your main piece of evidence in a death penalty case, and say, "okay, you get up there and talk about what you did and what graves did, but i'm not going to ask you about your wife." you can't do that. >> reporter: why in the world would you agree not to ask him about her? >> well, i needed his testimony. >> reporter: and sebesta points out the deal was approved by a judge and the defense never questioned it. >> that put on the record, i did put on the record. >> reporter: the indictment against carter's wife was later dismissed due to a lack of evidence. and siegler never bought i

. >> reporter: otto hanak tried to confirm the testimony from sebesta's jailhouse witnesses. >> we can't find anybody that can positively say, in court or in this room, that "i heard anthony graves say this, i heard robert carter say this." >> reporter: he looked into roy reuter's knife. >> the blade is flimsy. >> reporter: and, according to hanak, a knife this flimsy could not have caused the kind of wounds to the skulls that were found on some victims. >> i personally do not believe that that blade is strong enough, nor is this knife made well enough to go through human skulls. >> it's a switchblade knife. they're made pretty sturdy. >> reporter: d.a. charles sebesta had argued graves' identical knife had inflicted 66 stab wounds the night of the murder. >> there's no doubt that that knife could have survived that. we had texas ranger testimony that it could have done it. >> reporter: but hanak, who is a