i m glad everything s okay. we ll disregard for you. have a good night. reporter: it was probably the last time peggy s voice was heard by anyone except her killer. police were convinced still are convinced peggy was letting in someone that she knew. susanne? maybe. but why would she use a tracfone to get her mom to open the door in the middle of the night? she wouldn t have to let me in. i have a key. and i know the how to work the alarm. reporter: right. so if you wanted to kill her, you could have waited until she went to sleep and went in. reporter: unlocked the door and went in. reporter: disarm the alarm. there you go. there you go. reporter: police had warrants for all the family members phones. and a few weeks later they had boxes of records to comb through. detectives analyzed susanne s first. what could you tell about susanne from her cell phone records? a lot. reporter: investigator robyn arias from the westchester county d.a. s office spe
reporter: and on the day of peggy s murder that day was like every other day in susanne s life. there was no change for that particular day. reporter: and you d expect to see a change if somebody was in the process of committing murder for the first time? correct. correct. reporter: suggesting she s innocent? either she s innocent or she has another phone. but there certainly wasn t communication that indicated that something was going to happen. reporter: as hot as detectives were on susanne s trail, they had never stopped looking at the other members of peggy s immediate family. you talked to peggy s son jim and his wife diana right after the murder? yes, when they came up. reporter: they live in florida? correct. reporter: were they in florida at the time of the murder? jim was in florida. and diana said she was in d.c. reporter: why was she in d.c.? she said there was a family wedding. reporter: and the records backed that up. when robyn arias looked
my sister-in-law used to call every morning. my mother would be on my phone with me and say, oh, i gotta go. diana s calling on the other line. reporter: diana was a stay-at-home mom with two kids, leah and harris. peggy doted on her grandchildren and would fly them up to new york to spend summers and holidays. detectives had already confirmed that diana s cell phone had been in washington, d.c., at the time of the murder. but when phone analyst robyn arias looked more closely at diana s calling pattern something seemed off. when she was in d.c. her activity was just all over the place. kind of the frenetic feel. there was definitely something going on. reporter: now arias looked at who diana was calling, putting names and faces to the numbers on her phone. she noticed diana suddenly seemed have a lot of new friends in washington, d.c. a lot of people just popped
florida. diana s phone records checked out, too. where was diana s phone during that time? in d.c. reporter: that s it? didn t move. did not move. the phone went to d.c., went back to florida. reporter: reasonable to assume that diana never left d.c.? absolutely. reporter: but you re smiling. there was just a break. the pattern just was off. reporter: diana s records were speaking to arias, and detectives were about to get a break that would shift the direction of the entire investigation. let s just say, this case was about to go south. that secret burner phone, who bought it? who used it? get ready for a whole new circle of suspects. so what s going on here? how many people are involved in this? that s the question of the day.
up in diana s life for a very brief moment. reporter: arias calls them frequent users, people diana was calling repeatedly. what was also interesting to me about these frequent users is that they just had such different lives. reporter: diana was a suburban mom, and some of these people, well a lot of them had criminal histories living in d.c. reporter: remember, diana had been in d.c. for a wedding. maybe these people were, you know, those friends of the groom you have to invite? so detectives got the guest list. none of the high frequency callers were at the wedding. none of those people. reporter: and when arias looked at diana s phone records on the night of the murder, friday night into saturday morning the time of the homicide there was very little activity on her phone. like eerily quiet. reporter: what did that mean? diana s phone had been in d.c. that looked like a dead end.