In 2014 people were horrified after a story broke detailing how two then-12-year-olds had been accused of stabbing a friend 19 times, in service of a fictional online boogieman. The friend survived.

The two girls are being tried as adults, and one pleaded not guilty earlier this year on grounds of mental health. If convicted, both will face decades in jail.

HBO announced a documentary earlier this year looking into the case of Slenderman, the faceless creation of horror site Something Awful the two girls were hoping to act as a proxy for, and the first trailer has just dropped.

We know Slenderman is not real, and was created by Eric Knudsen, but it still looks pretty terrifying.

The documentary, looking at Slenderman and the case of the two accused girls Morgan Geyser and Anissa Weier, is expected to air in 2017.