and it goes to chief investigator andy rosenzweig.nt, he's extremely detail-oriented. >> when you look for a case, what did you look in the folder to say, this one looks good to go? >> we looked at a case that, you know, presented a challenge, that we thought perhaps other agencies wouldn't be equipped to do as well as us. >> what andy rosenzweig did initially to further this investigation was that they knew he was a pilot, and they began canvassing various airports to see if they could find any evidence as to whether he had rented or flown a plane on july the 7th, 1985. >> they started out looking at private aviation companies in new jersey. the second choice was essex county airport. and they struck gold. >> so they came here, went through that door? >> went through that door, and they said, yes, as a matter fact, we do know robert bierenbaum. do you have records of him flying? yes, we do. robert bierenbaum, the day his wife disappeared, drove to caldwell airport sometime in the afternoon. flew a plane for over an hour and a half. r

that guy was andy rosenzweig, the chief investigator of the manhattan district attorney's office. >>orter: the d.a.'s office has just created a cold case unit. rosen zweig assigned steve saracco and dan bibb to the bierenbaum case. >> the first thing that stood out to me when i reviewed the file were the flight records. there's the explanation why gail is not around anymore. >> that coupled with his visits to his psychiatrist dr. michael stone. i called stone, cold-called him, and he said of course he killed her, dr. bierenbaum's a dangerous psychopath, this case has been burning on my brain. >> reporter: in the summer of 1998 gail's body was exhumed, but the dna of that torso did not match gail's. >> i am so devastated. and i looked up at dan and at steve and i said, "now you better get a conviction." >> in late november of '98 we decided to send investigators to north dakota to see if we could get some kind of statement. >> he's feeling as safe as you possibly can. all of a sudden now he sees these guys from manhattan telling him we're here because we're investigating -- reinvestig