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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 ....

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