Leiden’s hbo college was evacuated by police on Friday afternoon following a bomb threat. The building was cleared of some 300 people and searched for explosives.

A police spokesman told the NRC he could not confirm if there was a connection with a threat to shoot a teacher at a school in Leiden made earlier in the week.

The youth believed to be at the centre of that threat, which led to all secondary schools in the city being closed on Monday, is now thought to be on his way back to the Netherlands from Costa Rica.

His return is voluntarily but he is being accompanied by officials, according to media reports.

Meanwhile police have been questioning a friend of the suspect and have taken away a computer for examination, website nu.nl reported.