The threats, which came in the lead-up to Halloween during the great clown panic of 2016, from accounts billing themselves as “killer clowns” led to intensive surveillance, according to records from Washington D.C.’s Metropolitan Police Department (MPD).

Clown sightings were recorded all over the U.S. in 2016, with the craze eventually coming to the attention of the police.

An October 3, 2016, document, entitled Social Media Clown Threats, obtained by The Guardian, reportedly laid out measures taken by authorities over the prior four days in relation to “threats coming from accounts created by unknown persons with profile pictures of clowns” on “the popular Social Media sites today like Facebook, Instagram, Twitter, etc.”

The report was found in a trove of police documents stolen and published by the ransomware attack group Babuk and later redistributed by the transparency organization Distributed Denial of Secrets, The Guardian reported.

The files referenced several non-specific threats made from an Instagram account, “snappytheclown_,” and a Facebook account, “killerclownamber,” to a large number of public schools in the D.C. area.

These threats had “been garnering the attention of many School Administrations and have been a cause of concern for many parents,” the report said.

Particularly threatening posts recorded from “snappytheclown_” included a photo of two men dressed in sinister clown outfits alongside text reading “Cardozo and Bell, here we come,” seemingly in reference to two public schools in the D.C. area. “The attack will be Monday at 3.30 PM after I prove you will join me in humanity’s annihilation,” the post allegedly reads.

The document also detailed alarming reports from students, one of whom shared a screenshot of an Instagram post from an account, “dmv_clowns,” which claimed that they would be “coming to” that school along with seven others.

In another incident, police said they received a report from an eighth-grade student who “stated that she definitely saw two individuals wearing Clown Masks while they were walking on the dirt path from Somerset heading towards Alabama Ave near the Liff’s Market”, according to a 14-page document seen by The Guardian.

Police reportedly made attempts to obtain warrants to get account information for several clown Instagram accounts and Twitter’s deletion of an account, @joetheclown.

Newsweek has contacted Washington D.C.’s Metropolitan Police Department for comment.

According to The Guardian, the “uncanny valley” effect, a phenomenon where we’re unnerved by things that aren’t human but have a human-like appearance, may be responsible for some of our clown fear.

Clowns put on makeup to exaggerate the features of their face, they wear silly and odd costumes, and paint smiles on their faces, all of which sets them apart from regular humans. Additionally, we subconsciously pay attention to the way other people walk, their posture and their stance. A clown exaggerates these movements and can move inconsistently, a combination that can be unsettling to us, according to The Guardian.