No one knows why good and evil cross paths. Why simply stopping to pick up a snack for a boyfriend might turn fatally dangerous. Or why a roadside convenience store became a spot where innocence was lost, where a college sophomore came face-to-face with a remorseless killer.
Melanie Goodwin lived nearly all her 19 years in front of the camera -- a born actress in what would turn out to be a tragedy of Shakespearean proportions.
"When she was a little girl, like 2, she'd be making faces in front of the mirror and just entertain herself for hours," her mother, Peggy Goodwin, told ABC News' Jim Avila. "So we started her in voice lessons and theater classes when she was about in third grade."
Growing up in Arlington, Texas, Melanie Goodwin's best friend, Demyia Pridgen, was always there to help her practice. "As kids, we loved to play," Pridgen said. "We had great imaginations. Melanie always loved to sing and dance, and to laugh."
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Goodwin's father, Glenn, never missed one of her performances. His favorite part of hers was Cinderella.
"She was just the most beautiful godmother you could ever imagine," he said. "She walks out with a crown on and her scepter -- you could just hear the audience gasp."
And her fairy tale was not just on stage: She was living one. A communications major at the University of North Texas, Goodwin had found a boyfriend, Ale Valencia, with leading-man looks and a heart to match.
"We were just two fools in love who were best friends and couldn't get enough of each other," Valencia, now 23, said.
He said he knew Goodwin was the woman for him, forever.
Her deeply religious family was close. She had an older sister and brother who adored her, and she was a star at home. "And, of course, she was my baby," her father said. "So you know, the baby's the baby, and she's my girl."
Her full life was backed by a supporting cast of many fast friends.
"And that's what makes this so hard -- you just can't imagine something like this happening to such a beautiful person," best friend Pridgen said.
Crossing Paths: 'Oh No, I Don't Think So'
The state-of-the-art Quik Trip convenience store in Denton, Texas, has four full-time cameras watching customers, the registers and the sidewalk out front. It was the cameras whirring away in the middle of a September 2007 night that gave Detective Greg Fraid of the Carrollton Police Department the first clue to the identity of the alleged culprit.
"The first thing that stands out in our mind is a male that is just kind of walking up and down the outside of the store," Fraid said, describing the tape.
For an hour and a half early that morning, long before Melanie Goodwin stopped by for a snack to take home to Valencia, Ernesto Reyes, 20, hovered near the counter, at one point convincing the clerk to let him use the phone. He was trying to get his estranged girlfriend, other friends -- anyone -- to give him a ride and a place to stay, according to Dallas County prosecutor Andrea Handley.
Handley, who has watched the tape over and over again, said, "He'll hang up the phone. He'll walk around. He'll pace back and forth. He's just flat out loitering.
"He has no money, and he asked the clerk, 'Hey, can I sleep here?' And he said, 'You can't sleep at this store. And by the way, buddy, you might not want to hang around here anymore.'"
He was outside the store when Goodwin, dressed in a skirt and top, came in, as seen on the video. She headed right over to the snack aisle for the Cheetos her boyfriend asked her to pick up, and, then to the dairy case for chocolate milk. The clerk was busy but remembered Goodwin had gone back to the restroom -- and that's when she met the loiterer, Handley said.
"And he remembers as best he can that the defendant was, in fact, asking her for a ride," Handley said, referring to the clerk. "And you can very faintly hear it on the tape. You can hear him say certain things like, 'My truck broke down,' or 'I would walk but these shoes aren't good. And it's just a quarter of a mile. It's just up to McKinney Avenue.' And you hear her saying, 'Oh no, I don't think so.'"
The next day, police would begin looking for suspect Reyes.
Visit the "Primetime" Web site Tuesday for Part II of Melanie Goodwin's story.