In this May 31, 2014 photo, rescue workers take the 12-year-old stabbing victim in the so-called “Slender Man” case to an ambulance in Waukesha, Wis. (Abe Van Dyke/AP)

Two 13-year-old girls charged with stabbing a classmate 19 times and leaving her for dead in the high-profile “Slender Man” case will be tried as adults, a Wisconsin judge ruled Monday.

Waukesha County Circuit Judge Michael Bohren’s decision to keep the girls in the adult court system has major implications for Morgan Geyser and Anissa Weier, who are charged with attempted first-degree intentional homicide and could face sentences of up to 45 years each, the Milwaukee Journal Sentinel reported. The Washington Post is naming the juvenile defendants since they will be tried as adults.

“This was an effort to kill someone, not a mistake by hitting someone too hard,” Bohren said, ABC affiliate WISN reported.

[Pre-teen girls accused of stabbing friend 19 times to honor mythological creature]

Advocates of criminal-justice reform have kept a close eye on the case and believe the girls should be treated by the system as minors. “Anything else is legal fiction,” National Juvenile Defender Center director Kim Dvorchak told the Journal Sentinel before Bohren’s decision.

The horrific 2014 stabbing attracted national attention in part because of its connection to the Slender Man, a mythological creature and Internet meme born out of an obscure online forum in 2009. The girls told authorities that they hatched a plot to kill a friend during a birthday slumber party in May 2014to prove their loyalty to Slender Man; they also said Slender Man had threatened their families, according to the criminal complaint.

Geyser and Weier were 12 years old at the time of the alleged attack; a passerby found the victim bleeding in a wooded park, and the girl survived.

[The complete, terrifying history of ‘Slender Man,’ the Internet meme]

Shortly after the stabbing, authorities found Geyser and Weier walking toward Nicolet National Forest, where they said they hoped to join Slender Man in his mansion. One of the girls had a five-inch blade knife in her backpack, according to the criminal complaint.

The girls were initially charged as adults, per Wisconsin law. Prosecutors also argued that the girls behaved like adults in spending months in plotting the killing of their friend, which they described in court filings as “a very adult offense,” adding that the girls “should remain in adult court to face the consequences.”

[‘Slender Man’ Halloween costumes outrage community where 12-year-old girls allegedly stabbed classmate]

Lawyers for Geyser and Weier presented arguments during two separate hearings earlier this year in an effort to get them returned to juvenile court, where they could have received a maximum sentence of five years. If convicted in adult court, they would remain in a juvenile facility until they turned 18. The girls would receive better mental health treatment in the juvenile system than in the adult system, their attorneys argued.

Geyser was diagnosed with early onset schizophrenia during court competency evaluations, and she still believes in the existence of the mythological Slender Man and fictional characters such as Harry Potter. She is opposed to taking medication because she believes it  would stop her ability to talk with these “friends,” the Journal Sentinel reported.

[‘Slender Man’ recedes in Wisconsin stabbing case as mental health becomes issue]

Geyser’s attorneys argued that their client’s condition would worsen in adult prison, the Associated Press reported. She “is not the hardened, irascible offender who… needs to be taught a lesson through adult court placement,” attorney Anthony Cotton wrote in court filings.

Experts testified during a May hearing that Weier had a delusional disorder in 2014, that she is remorseful and that she wants to get better. Both the stabbing victim and Weier told authorities that Geyser did the stabbing, the Journal Sentinel reported.

The defense had to clear a number of hurdles in order to get their clients’ cases transferred to the juvenile system, including proving that moving them wouldn’t “depreciate the seriousness of the offense.” Reporters in the courtroom tweeted the judge’s reasoning as he delivered his decision:

Both defendants will be arraigned on Aug. 21, according to court records.