Dutch officials pulled armed police from secondary schools in the western city of Leiden on Wednesday as they lowered the level of an alert over an online threat to carry out a school shooting.
The threat to "shoot my Dutch teacher and as many students as I can" made on a US-based website over the weekend led to all secondary schools in the university city being closed on Monday and police being deployed.
"The concrete threat has diminished," the city said in a statement, adding that "the suspect has been living abroad for some time".
It was therefore decided "to end the current monitoring at secondary schools in Leiden".
Police are now focusing their attention on an unidentified male suspect living in Costa Rica, believed to be a Dutch citizen.
He was kicked out of a Leiden secondary school after a fight with a teacher, had an "interest in weapons and had held a presentation about school shootings," police learned.
The man recently told his Dutch family he was living in Costa Rica which was also confirmed by computer experts helping the police, the statement said.
"The police are working hard to track his exact address and are doing everything possible to contact the suspect to ensure he returns to the Netherlands," it said.
Authorities in Leiden had decided late Sunday night to close secondary schools to thousands of pupils after a tip-off by Swiss police following the threat.
"I will shoot my Dutch teacher and as many students as I can," said the anonymous message in English on the 4chan.org website.
"It's at a school in the Dutch city of Leiden" it said, chillingly adding "for more proof, I will be using a 9mm Colt Defender".
"Oh, and I'm using a proxy, the police is not gonna find me before tomorrow," the message ended.