A 16-year-old student who threatened earlier this year to go on a shooting rampage at his school stabbed three students and a janitor on Thursday, the police said. All four victims at the vocational school in northern Finland were in stable condition in a local hospital, the police said. Deputy Police Chief Arto Karnaranta said that the suspect was arrested in Oulu, 370 miles north of Helsinki, and that he had admitted to the stabbings but did not disclose a motive. Chief Karnaranta said the suspect had made online threats against the school in February, “saying that he would ‘kill the whole school’ if he had a gun.”