Parents of Accused Teen Stabber in 'Slender Man' Case Speak Out for the 1st Time

The parents of Anissa Weier, one of two 12-year-old girls who allegedly stabbed another girl 19 times in an effort to impress fictional internet character "Slender Man," said today they were as shocked by the 2014 attack as everyone else.

"It was really kind of surreal from the time I got the phone call," Bill Weier, Anissa's father, told "Good Morning America" today of his reaction to news of his daughter's alleged connection to the incident in the woods of a Milwaukee, Wisconsin, suburb. "I think surreal is the best way to describe it."

Anissa Weier and Morgan Geyser have been charged with the attempted murder of Payton Leutner, who was purportedly their friend at the time of the attack, and are expected to be tried as adults this year in a Wisconsin court.

They remain in custody after a judge last year denied their motions for bail reductions. They have pleaded not guilty to the charges on grounds of mental illness.

If Morgan and Anissa, who's now 15, are convicted in the adult court system, they could each face up to 65 years in prison.

The injured Payton Leutner, also 12 at the time, purportedly crawled to a road where a cyclist found her and alerted authorities. She was rushed to a hospital, and survived.

The interview with Anissa's parents comes in advance of a forthcoming HBO documentary, "Beware the Slenderman," which will air for the first time next Monday.

"This isn't a 'whodunit,'" Irene Taylor Brodsky, the director of the documentary, told "GMA" of the film. "We know they did it. It's really a 'howdunit.' It's a 'whydunit.'"

The Weiers' described their daughter as being remorseful and don't believe she should be tried as an adult because they say the laws are not sufficiently up-to-date with the science of juvenile brain development.

Children as young as 10 can be tried as adults in Wisconsin.

Kristi Weier, Anissa's mother, told "GMA" that when HBO approached her, she agreed to participate in an effort to help other parents who might be caught off guard by what their children are consuming online.

"If we were not able to help our daughter," she said, "we might be able to help someone else."