A teenager was jailed for five years yesterday for his involvement in the kidnapping of an 11-year-old schoolboy who was later murdered. Chan Chi-sin, for whom a $1.4 million ransom was paid, was strangled hours after he was snatched outside the American International School on July 11 last year. Yu Ka-fai, 17, was found guilty of conspiracy to kidnap but cleared of any involvement in Chi-sin's murder. He was also acquitted of blackmailing the victim's father. Sentencing Yu yesterday, Mr Justice Thomas Gall said the teenager's role in the crime showed a 'callous disregard' for the intended victim.