Elizabeth Smart's little sister was the only eyewitness to her sister's abduction.

Mary Katherine, 9, watched as an armed man entered her bedroom and led Elizabeth away at gunpoint.

Then she waited.

According to police, the kidnapper threatened to hurt Elizabeth if Mary Katherine told anyone about the abduction.

So she sat in her room for as long as two hours before telling her parents who, when told, called 911 at 4:01 a.m.

Certified forensic psychologist Gerald P. Koocher said it is remarkable the child notified the parents as soon as she did.

Koocher, dean of Health Studies at Boston's Simmon's College and a faculty member at Harvard Medical School, pointed out that in other scenarios such as sexual abuse, a child will refrain from telling on or speaking about the incident for years if there is a threat to hurt other members of the victim's family.

From her brief encounter and with the help of police examiners, the soon-to-be fourth-grader gave a description of the kidnapper: a white male, possibly in his 30s, about 5 feet 8 inches, with dark hair and a medium build.

The morning of the incident, Salt Lake Police Sgt. Dwayne Baird said Mary Katherine "saw a little bit of what was going on, but she couldn't see him real clearly."

A few days later, authorities brought a child forensic specialist to Salt Lake City to re-interview Mary Katherine, but the description didn't change, and any new information found in the interview, if there was any, was not reported to the media. To date, authorities say Mary Katherine has been interviewed four times, all along insisting her testimony remains consistent.

"Police will have a hard time gauging the amount of time that passed before the girl told her parents," Koocher said. "Children gauge time differently."

But Koocher said a child's testimony of the event should be considered as credible as an adult's.

"Any person, a child or adult, in a situation like this is subject to a lot of stress, but the facts of what took place will be accurate," Koocher said.

But the details might be a little distorted, he said.

"A child laying down is going to have a hard time telling just how tall a man is who is standing over her."

In questioning children, an investigator must be careful not to ask pointed questions such as, "Was the man about the same height as your father?" Koocher said. But at the same time, investigators must be quick in gathering testimony.

Over time, a person can fabricate thoughts and experiences, Koocher said.

"Most people don't actually have memories of being 3 years old; instead they remember what their parents told them and fabricate the scenario in their own minds."

But Koocher said in the disappearance of Elizabeth, her sister could not have been coached by an adult to produce the testimony.

"Kids are not good secret keepers unless they feel threatened, and in this case it doesn't appear there would have been a lot of time for coaching. If there were, after four separate interviews there would be some level of inconsistency," he said.

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