Dutch police said they advised schools in Leiden to close because of a threatened mass shooting, then arrested a former student of a school in another city, UPI reported. Authorities had closed 22 schools Monday after police advised that an anonymous website threat told of plans to shoot a teacher "and as many students as I can." The person arrested, who was not identified, formerly attended the British School in the neighboring city of Voorschoten, the BBC reported. The writer said he or she would be carrying a 9mm Colt Defender and a note, "which will explain why I did it." The British School issued a statement that said the suspect left its senior school in October 2011 because of inappropriate behavior. Leiden Mayor Henri Lenferink said the decision to close the schools for the day was made because "it [the threat] could just be a morbid joke but we didn't want to take any risk."