A MAN convicted of supplying nearly 300 grams of heroin has walked free from court without serving a day in a NSW prison for the crime he committed more than 21 years ago.

The man, who cannot be named for legal reasons, claimed he was set up in a drug sting by corrupt police, and said the transcript of his interview with police - recorded only on a typewriter - was falsified.

One undercover officer involved in the sting, Timothy Charles Rochford, was later convicted of supplying 10 kilograms of cocaine, District Court Judge Jonathan Williams said as he sentenced the man on Friday.

"I'm somewhat concerned as to how much of Mr Rochford's evidence should be accepted as being precise," Judge Williams said, but added he was unable to determine if police fabricated evidence against the man.

He said the man was 17 at the time of the offence and should have been dealt with as a juvenile, even though he had frequently used the birth date of his dead older brother and told police he was older. But he was a bodybuilder and used steroids, which could have given him an older appearance.

The then youth was arrested in May 1987 with 279 grams of heroin wrapped in a newspaper which he had just been handed by an associate.

He was granted bail but left Australia later that year for the United States, where he was arrested 10 years later on charges of making a false statement on a passport and firearms application.

After he served a 10-month sentence, he was detained because of the outstanding NSW warrant. NSW police were not interested in extraditing him because of the costs, Judge Williams said, and the man was not arrested when he returned to Australia voluntarily in 2002. However, when he was stopped for a traffic offence in February 2005, police arrested him and charged him with the 1987 offence.

At his trial early last year, the man told the jury he believed the newspaper contained steroids and knew nothing of the heroin.

He also claimed police had beaten, threatened and humiliated him and had advised him to leave the country.

The jury convicted him in February last year, but the verdict was appealed after it was discovered the prosecution had laid the wrong charges.

When sentencing him, Judge Williams said he would take into account the delays in the case, the nearly two years spent in immigration detention in the US, his young age in 1987, his ageing mother, and his good prospects of rehabilitation.

He sentenced him to a minimum of two years in prison, backdated to expire on Friday, and ordered that he be released to parole for one year.