Sometime after stabbing a classmate in the Wisconsin woods, Morgan Geyser sat in a police station with a detective who was trying to figure what happened

Hours after stabbing a classmate in the Wisconsin woods, Morgan Geyser sat in a police station with a detective who was trying to determine what had led up to the nearly-deadly assault.

“What were you trying to do with her when you stabbed her?” he asked Geyser, who replied:

“Kill her. I might as well just say it. We were trying to kill her.”

The interrogation is shown in video obtained by ABC News for a Friday night episode of 20/20 that focuses on the case. An exclusive clip of the show is above.

In the preview, Geyser’s mom, Angie, reacts to the footage of her daughter, then a pre-teen, discussing the stabbing of Payton Leutner.

• Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter.

“The interrogation is very difficult to watch because that’s not my daughter saying those things. That’s not the way that she speaks, that’s not the way that she acts,” Angie tells ABC News’ David Muir.

Angie says later in the clip, “[Morgan] appears to have no remorse for what’s happened and she just talks about it in such a flat manner.”

On May 31, 2014, according to police, Geyser and Anissa Weier lured Leutner to a park in Waukesha, where she was stabbed 19 times. Authorities said Geyser and Weier claimed the attack was an attempt to please the fictional Internet horror character “Slenderman” and protect their families from him.

Anissa Weier (left) and Morgan Geyser after their arrests in the 2014 Slenderman stabbing in Wisconsin
| Credit: Waukesha Police Department
Morgan Geyser
Morgan Geyser (left) in court in September 2017
| Credit: Michael Sear/Milwaukee Journal-Sentinel/AP

Geyser stabbed Leutner while Weier urged her on, investigators said. But Leutner, who was left for dead, survived and crawled to a nearby bike path, where she was spotted by a passerby who called 911. All three girls were 12 years old at the time.

In August and October of last year, Weier and Geyser, respectively, pleaded guilty to their roles in the attack. They had been charged as adults with attempted first-degree intentional homicide. Weier pleaded to being a party to attempted second-degree intentional homicide while Geyser pleaded to the original charge.

• For more compelling true crime coverage, follow our Crime magazine on Flipboard.

Weier was found not criminally responsible after a jury determined she was mentally ill at the time, and a judge ordered her committed to a treatment facility for 25 years. As part of Geyser’s plea agreement in the fall, prosecutors did not contest that she, too, was not criminally responsible due to her mental illness. Her family has said she was diagnosed with early-onset schizophrenia.

In a statement at the time, Leutner’s family said they were happy to avoid a trial, noting, “Though we do not believe that an institution is where these attempted murderers belong, the current legal system does not favor victims in this situation.”

Girls Stabbing Plot
Anissa Weier (right) in court in December 2016
| Credit: Michael Sears/Milwaukee Journal-Sentinel/AP

This week, a judge will rule on how long Geyser will also be committed, according to ABC News. Prosecutors are seeking 40 years.

In Friday’s 20/20 episode on the case, ABC will speak with the families of Geyser and Weier as well as the case’s prosecutor, Kevin Osborne.

Speaking to PEOPLE for a story last year, Weier’s mother said the motive for the attack may never be fully knowable.

“The only person that knows why they did this is 12-year-old Anissa and 12-year-old Morgan,” she said. “Those children, basically, don’t exist anymore.”

20/20‘s episode on the Slenderman stabbing airs Friday (10 p.m. ET) on ABC.