Secondary schools in Leiden reopened on Tuesday after officials said they were taking the threat of a shooting less seriously.

All secondary schools and mbo colleges in the city were closed on Monday after someone posted a message on an internet board saying they planned to shoot a teacher and as many pupils as possible.

But the fact no location was named and no motive was given means the threat has now been downgraded, the city’s mayor told a late-night radio show.

Guarantee

Nevertheless, schools will be under extra surveillance today because experts cannot guarantee there is no threat, mayor Henri Lenferink said.

Police on Monday arrested a former pupil at the British School in Voorschoten in connection with the incident but are still looking into whether or not he placed the threat on the international website 4chan. The trail currently leads to Costa Rica.

The boy was expelled from the British School in October 2011 and is known to social workers, a source told Radio West.