see. you know who we are, right? yeah, why wouldn t i know who you are? okay. just making sure. steve and earl. reporter: and she knew why they were there. you think i killed my mother-in-law. is that what you re telling me? reporter: yes, it was, and after five months, their investigation was about to end. you re under arrest for the murder of peggy nadell. i did not murder my mother-in-law. reporter: that same day, another team arrested andrea benson in d.c. detectives lorence and cole-hatchard were confident they had the right people in custody and that susanne was finally off the hook. she heard the news from relatives. they said they arrested diana for my mother s murder. and that there were other people involved in it. and i was shocked. reporter: what did she look like? oh, god. her eyes were probably about as big as the headlights on a volkswagen beetle. and her instant reaction was, i knew it. i knew it. reporter: susanne says her
reporter: much like the fictional character peggy olson in the hit series, mad men, the real life peggy broke the glass ceiling at xerox and became a rare member of the executive boys club. anne martin was in that club too. you didn t have too many female managers. and peggy, she rose very quickly because she was very intelligent. reporter: and always well-dressed. peggy wore a lot of black. she loved to dress and wear the latest fashions. reporter: unlike her fashionable mom, susanne, was a blue jeans and t-shirt kind of girl. susanne how do you explain susanne? she s quirky. she s outgoing. she athletic. reporter: darcy greenberg is one of susanne s best friends. she s spontaneous. she s talkative. she also likes to be close to home. reporter: after college, she came back to rockland county and went to work at xerox herself. one night in a bar susanne, then
it was her daughter-in-law diana. detectives knew that diana s friend, karen hamm-samuel, had bought the tracfone that called peggy s house just before she was murdered. diana had told police from the beginning that she d been in washington, d.c., to attend a wedding. but her alibi was wobbly. diana couldn t account for her time in d.c. she hit washington at about 9:30 and didn t reappear again until about 8:00 the next morning. reporter: so detectives called diana, asking her to fill in the gaps. i just have to confirm that you were up in washington. is there somebody i can talk to? what do you mean? we had to keep it real simple with her. listen. we just want to get you cleared. where did you spend the night? reporter: what did they not tell diana? detectives had a warrant and they were tapping her phone. police now sat back and listened as diana made multiple calls to
assistant d.a. moran didn t think so. peggy would never have let a stranger like andrea benson into her house. so that had to be a friendly voice on the phone? yes. reporter: detectives thought that voice might have belonged to diana, but they had nothing to put her on the scene, in peggy s house. at this point, is susanne off the hook? diana is now the higher suspect. susanne wasn t off the hook. reporter: they could be in this together? correct. yes. that s where it was. reporter: because they both benefited. absolutely. yes. reporter: now eight weeks into the investigation detectives still didn t know who had killed peggy nadell. with suspects in florida, d.c., and new york, detectives came up with a new strategy. and their phone expert liked it a lot. gutsy. like, i mean, a lot of people don t go to those lengths on a homicide case. i thought it was a brilliant strategy.
reporter: soon clarkstown police detectives stephen cole-hatchard and earl lorence were on the scene. they noticed that susanne looked a wreck, standing in front of the house in the snow. susanne is in the driveway, at the foot of the driveway, kind of pacing, looking rather frazzled. reporter: she told detectives what she told the 911 operators, that peggy tripped over the cat. her mother must have tumbled down the stairs and stabbed herself with the knife. reporter: while detective cole-hatchard stayed outside with susanne, detective lorence went inside the house. this is police video of the scene taken that morning. lorence knew right away, this was no accident. no way did she fall down the stairs and trip over a cat. reporter: detective lorence saw peggy had been strangled, then stabbed. and it also looked as if she d been beaten with a statue head found under her body and a gold metal ball near her hand.