Watch the trailer for HBO's documentary Beware the Slenderman

It's the story of two Wisconsin 12-year-olds who are accused of stabbing their friend 19 times.

The story of how Slender Man ended up at the center of a disturbing stabbing case in Wisconsin is being examined in a documentary.

The first trailer for HBO's Beware the Slenderman was released. The film will premiere Jan. 23, 2017.

A creature of fantasy. An act of savagery.

Beware the Slenderman premieres January 23 on HBO.

Posted by HBO Documentary Films on Thursday, November 10, 2016

The film will explore why prosecutors say two young Waukesha girls stabbed their 12-year-old friend in 2014 as an apparent tribute to the Slender Man, a fictional character they read about online, the Washington Post said.

Their victim survived, and the girls were charged as adults with attempted murder, but have pleaded not guilty by reason of insanity, Waukesha Now reports. The girls are expected to appear in court Friday at 1:30 p.m. for a "status conference," according to the Waukesha County court calendar.

HBO's documentary – which uses home videos, interviews with family members and the girls' taped confessions – won't focus on the girls' guilt or innocence, but will look at "the court's deliberation whether the girls should be tried as adults or children," director Irene Taylor Brodsky said in a statement to Buzzfeed.

Mashable says the documentary raises an important question: "With dangerous, impressionable content lurking beneath the surface of the web, how much do we hold children responsible for what they find?"

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