A 15-year-old boy was sentenced Wednesday to a maximum of five years in prison for his guilty plea to shooting two subway riders to death and wounding another person.

"He got a kick out of blowing them away," said a cousin who was with him when the boy killed one rider.

The two killings took place in separate incidents in March on a subway when the boy, who was not identified because of his age, shot two male passengers in the head during holdups.

Between the two killings, the boy shot subway motorman Anthony Lamorta, 30, in a subway yard. Family Court Judge Edith Miller sentence the boy, who is from Harlem, to five years in prison with a minimum 18 months in a secure facility, the maximum she could impose under the juvenile offenders law.

"He's the most violent kid I've ever seen in Family Court," said one prosecutor. "He's a cold-blooded killer."

Locked up in the Spotford Juvenile Detention Center, the boy warned another inmate. "I'll kill you if you sit down next to me." He stabbed the inmate in the neck with a fork. The boy once bragged of having a record of eight robbery arrests which began when he was 9 years old.