SALEM – A Lynn construction worker already serving a federal prison sentence after being caught in New Hampshire with seven kilos of cocaine, has now admitted to selling heroin seven times out of Lynn in 2006 to undercover officers near a school.Juan Castillo, 42, who last lived at 36 Cottage St., #2, Lynn, changed his plea to guilty Monday in Salem Superior Court to trafficking over 14 grams of heroin, six counts of heroin distribution and three counts of distribution of heroin within a school zone.He was sentenced to serve seven and one-half years in state prison by Judge Howard J. Whitehead, but that sentence will run along with the 5-year federal prison term he is now serving.Assistant District Attorney Jean M. Curran said in October of 2005 police received a tip and a phone number involving a man selling drugs out of Lynn.On Feb. 9, 2006 arrangements were negotiated in which two bags of heroin was sold to an undercover officer outside a Chatham Street convenience store.Five more bags of heroin was sold for $100 on Feb. 15 and another five bags were sold on Feb. 23.On March 3, 19 bags, containing 17.64 grams of heroin, was sold for $1,800 to the undercover officer, Curran said.Then on March 16 and again on March 30 a bag was sold to the undercover officer.Three of the incidents on Feb. 9, Feb. 15 and Feb. 23 were on Chatham Street, within 1,000 feet of Lynn English High School.Castillo was arrested April 4 for the series of drug deals. He made bail and was then arrested in August 2006 in New Hampshire after being stopped for a motor vehicle infraction. Police found seven kilos of cocaine in the vehicle he was driving. He was given five years in federal prison with probation.Castillo will get time served dating back to when he was arrested in New Hampshire with the seven kilos of cocaine, which Curran strongly objected to.She told Whitehead that she felt it was a separate case and that he should serve the new prison term after he completes the federal term.Whitehead explained that although they are separate cases, there had been correspondence that inferred that Castillo was willing to plead to both cases at the same time.Castillo actually will serve just three years more before he gets out of prison, but will be on probation for another five years under his federal agreement.