reporter: 20 years went by. i still had to keep looking for what i had lost. reporter: but cathy had her. and she had him. i put a lot of faith in god. darren was his tool. and the killer? he never had a chance. this was everything to her. i fulfilled my promise. reporter: in the wee small hours of the morning, while the whole wide world is fast asleep, mary bennett is awake. not because she wants to be, but because some things stay with you, whether you want them to or not. and for mary bennett, it s the time 3:40 a.m. every day i wake up around that time. it s embedded in my brain. reporter: for more than two decades, that particular time has stabbed her in the heart, pulled her awake. it s an internal clock, permanently set to the worst day of her life. it began with a phone call, then a knock on the door, and news of something that should never have happened to this family, to this girl. when she would come inside the house, her favorite thing was,
dna. reporter: 20 years went by. i still had to keep looking for what i had lost. reporter: but cathy had her. and she had him. i put a lot of faith in god. darren was his tool. and the killer? he never had a chance. this was everything to her. i fulfilled my promise. reporter: in the wee small hours of the morning, while the whole wide world is fast asleep, mary bennett is awake. not because she wants to be, but because some things stay with you, whether you want them to or not. and for mary bennett, it s the time 3:40 a.m. every day i wake up around that time. it s embedded in my brain. reporter: for more than two decades, that particular time has stabbed her in the heart, pulled her awake. it s an internal clock, permanently set to the worst day of her life. it began with a phone call, then a knock on the door, and news of something that should never have happened to this family, to this girl. when she would come inside the house, her favorite thing w
reporter: 20 years went by. i still had to keep looking for what i had lost. reporter: but cathy had her. and she had him. i put a lot of faith in god. darren was his tool. and the killer? he never had a chance. this was everything to her. i fulfilled my promise. hello and welcome to dateline extra. i m craig melvin. cathy torres, the honor student was working two jobs to put herself through college and still made time for friends and family. but in the blink of an eye cathy would disappear. her case grew cold but cathy s mother never gave up. and neither did the tenacious detect who promised to find her killer. here is josh mankowitz. reporter: in the wee small hours of the morning, while the whole wide world is fast asleep, mary bennett is awake. not because she wants to be, but because some things stay with you, whether you want them to or not. and for mary bennett, it s the time 3:40 a.m. every day i wake up around that time. it s embedded in my brai
and she had him. i put a lot of faith in god. darren was his tool. and the killer? he never had a chance. this was everything to her. i fulfilled my promise. reporter: in the wee small hours of the morning, while the whole wide world is fast asleep, mary bennett is awake. not because she wants to be, but because some things stay with you, whether you want them to or not. and for mary bennett, it s the time 3:40 a.m. every day i wake up around that time. it s embedded in my brain. reporter: for more than two decades, that particular time has stabbed her in the heart, pulled her awake. it s an internal clock, permanently set to the worst day of her life. it began with a phone call, then a knock on the door, and news of something that should never have happened to this family, to this girl. when she would come inside the house, her favorite thing was, i m home. what s for dinner? even if somebody we just finished cleaning the kitchen, she d still ask, what s
and she had him. i put a lot of faith in god. darren was his tool. and the killer? he never had a chance. this was everything to her. i fulfilled my promise. in the wee small hours of the morning, while the whole wide world is fast asleep, mary bennett is awake. not because she wants to be, but because some things stay with you, whether you want them to or not. and for mary bennett, it s the time 3:40 a.m. every day i wake up around that time. it s embedded in my brain. reporter: for more than two decades, that particular time has stabbed her in the heart, pulled her awake. it s an internal clock, permanently set to the worst day of her life. it began with a phone call, then a knock on the door, and news of something that should never have happened to this family, to this girl. when she would come inside the house, her favorite thing was, i m home. what s for dinner? even if somebody we just finished cleaning the kitchen, she d still ask, what s for dinne