The Dutch town of Leiden shut down over 20 of its schools on Monday and one arrest has been made—all because of a threat posted to 4chan. Yes, international police forces are on to the Internet's most notorious message boards, and perhaps for good reason. "We have been informed that a former student of the British School in the Netherlands (BSN) has been arrested in connection to threats made against a Dutch school in Leiden," reads a statement from the school, while Agence France-Presse confirmed with police that a person was arrested. 

The person in question appears to be a poster on 4chan—the Internet forum known for epic trolling (i.e. sending pizzas to Chris Dorner's location or rigging online polls so that Taylor Swift could play a concert at a school for the deaf) and its infamous /b/ board. Now 4chan seems like a place police are looking out for shooting threats, and taking them very seriously. 

"Tomorrow, I will shoot my Dutch teacher, and as many students as I can," wrote the anonymous 4chan user in a posting (screencapped here) next to a photo of a briefcase of a gun and several clips of ammunition. The post continues: "I will be carrying a note ... which will explain why I did it.'" That's probably not the first or last shooting threat—real or unreal—that will be posted on 4chan, but it does come on the heels of a shooting in a Virginia mall on April 12 that occurred minutes after a 4chan user posted a threat providing details, gun types, timing, and more.

Swiss Police, the BBC reports, picked up that threat during weekend "Internet checks" and alerted Dutch authorities, which made the arrest on Monday.