Elizabeth Smart's Sister Discusses Kidnapping for First Time

July 20, 2005 — -- On a summer night in June three years ago, 9-year-old Mary Katherine Smart and her 14-year-old sister Elizabeth were asleep in their shared bedroom when an intruder slipped into the house through an open kitchen window. The man slipped into the girls' room and abducted Elizabeth.

Mary Katherine was the only witness to the kidnapping, but she didn't get a clear look at the intruder and couldn't provide investigators with enough details for a sketch.

Then several months later while flipping through a book, Mary Katherine had an epiphany that caused her to remember the name "Emmanuel." That was the name used by Brian David Mitchell, the man now accused of kidnapping Elizabeth. Elizabeth was living just 15 miles away from the family's Salt Lake City home with Mitchell, and his wife, Wanda Barzee.

Mary Katherine, who is now 13, is speaking out for the first time about the night of the kidnapping and the agonizing months leading to Elizabeth's recovery in an exclusive interview with Diane Sawyer on ABC News' "Primetime." The "Primetime" interview will air Thursday at 10 p.m. ET.

Mary Katherine awoke that night to see a man go over to her sister Elizabeth's bed and tap her. "I was sort of awake, and I saw this guy in my room, and I'm like, 'Who is he?' And I had no idea what he was doing in my room," Mary Katherine told Sawyer.

The man forced a frightened Elizabeth to get out of her bed and get shoes. Mary Katherine got up to tell her parents, but when she reached the bedroom door she saw the man forcing her sister down the hall. Terrified, Mary Katherine ran back to bed, where she stayed for two hours before getting up to tell her parents.

"I thought, you know, be quiet, because if he hears you, he might take you too, and you're the only person who has seen this," Mary Katherine said. "I was, like, shaking."

But Mary Katherine didn't get a good look at the intruder and only heard his voice. Weeks and then months passed as the police and community continued their frantic search for Elizabeth.