Mary Katherine interview tonight

It was while looking at a copy of "The Guinness Book of World Records" that Mary Katherine Smart remembered the name of a mysterious roofer she believed may have kidnapped her sister, Elizabeth.

That's one of the bits of information Mary Katherine talks about tonight during an interview on ABC News' "Primetime Live" with Diane Sawyer. The show will air a segment called "Brave Hearts" in which several young children, including Mary Katherine, are interviewed about witnessing horrific crimes committed against family members but were able to courageously help solve the cases.

"Primetime Live" airs on KTVX Ch. 4 at 9 p.m. Excerpts from that interview, which took place a few months ago, were released Wednesday.

It marks the first time Mary Katherine has spoken publicly about her sister's abduction, although some details about her realizations were included in the book "In Plain Sight: The Startling Truth Behind the Elizabeth Smart Investigation," by Tom Smart, the girls' uncle, and Lee Benson. Smart and Benson both work for the Deseret Morning News, and excerpts from their book were published by the paper in April.

Elizabeth Smart was abducted from her bedroom during the early morning hours of June 5, 2002. Elizabeth shared her room with 9-year-old Mary Katherine, who was the only witness to the crime.

Mary Katherine, now 13, talked for the first time to Sawyer about that night and the months that followed.

"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. I saw him come over to my side and then I saw him walk over to Elizabeth and he tapped her, and she's like, 'What is it?' And I guess she thought it was me," Mary Katherine told Sawyer.

Mary Katherine said she was amazed at how calm Elizabeth remained.

"If I was her, I would have like screamed my head off. I don't know how she did it," she said.

After Elizabeth was taken from the room, Mary Katherine got out of bed and peered out the entry of her room. She thought she saw the man again and went back to her bed, where she stayed for approximately two hours before waking her father.

"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 and you have to tell them so they know. I was like shaking," she said.

When Mary Katherine finally went to her father's room and told him, she said he raced straight to the girls' room, "and I told him you're not going to find her," she said.