While the accused attackers languish in the legal system, a probing documentary explores what led to their crimes.

The Beware the Slenderman documentary chronicling the May 2014 stabbing case that prompted a painstaking legal battle will finally come to Wisconsin soil at the Milwaukee Film Festival this fall. The film by Irene Taylor Brodsky premiered at SXSW in March, when The Austin Chronicle called it “one of those rare documentaries that you simply can’t not watch, horrific and deeply disturbing though it may be.” Slenderman explores to what extent the internet is responsible for the attack in which two 12-year-old girls stabbed their friend 19 times, trying to kill her to appease the Slender Man character they had read about online in fictional stories.

The movie has benefited from closer access to the girls’ families than any other media outlet, although Angie Geyser recently broke her silence with local media and gave a long interview to the Journal Sentinel. According to Variety, the film opens with a reenactment of the crime filmed like Blair Witch, the 1999 found footage horror picture. Horror studio Screen Gems is said to be working on a separate, fictional movie about the Slender Man character.

At some point, Beware the Slenderman is expected to debut on HBO. The cases of both girls remain locked in an appeal procedure, where the Wisconsin Court of Appeals has been asked to overturn a lower court judge’s decision to try them both as adults.

Read our full Slender Man feature, “In the Woods.”