A man convicted of drug trafficking and sentenced to life imprisonment has been acquitted of all charges by the apex court, in a split 2-1 decision.

Chief Justice Sundaresh Menon and Judge of Appeal Chao Hick Tin, in judgment grounds released yesterday, accepted Harven Segar's defence that he did not know, and could not reasonably be expected to have known, the nature of the drugs in his possession, on the balance of probabilities.

However, Judge of Appeal Tay Yong Kwang disagreed, saying Harven's defence was no different from the not-uncommonly heard plaintive plea of "I really didn't know they were drugs but I also didn't know what they were".

Harven, 23, a Malaysian, had been sentenced by the High Court in 2015 to life imprisonment and 24 strokes of the cane, after he was nabbed carrying three bundles of cannabis and 53.74g of heroin in a haversack on June 12, 2013.

He was convicted of drug trafficking and two other charges but escaped the gallows after he was certified as a courier. He was given the life term and 15 strokes of the cane for trafficking, and five years' jail and five strokes of the cane for each of the other two charges.

The maximum number of strokes the courts can impose is 24.

His sole defence at trial was that he did not know the bundles contained drugs and claimed they were passed to him by an acquaintance named Mogan in Johor Baru.

Mogan said he lost his passport and needed Harven to deliver the items to a friend in Singapore, the latter claimed.

Harven cleared Customs with the bundles in his haversack, but was nabbed in Jalan Besar.

The High Court found Harven failed to rebut the presumption that he knew the bundles contained drugs, although one factor in his favour was that he had given the haversack to a Singapore Customs staff without trying to hide anything.

On appeal against conviction, Harven's lawyers Ram Goswami and Cheng Kim Kuan argued that the High Court judge failed to give enough weight to their client's evidence in specific areas, and did not rule on his credibility.

The Chief Justice and Justice Chao said, among other things, that Harven's casual handling of the bundles "even at the Singapore Customs suggests an openness that is consistent with his genuinely not knowing the bundles contained drugs".

The judges said the fact that the bundles were heavy and wrapped in black tape need not have raised Harven's suspicion.

"To be fair to an accused like (Harven), it is important that the court does not readily assume that an ordinary reasonable person would be familiar with the practices of the drug trade," wrote Justice Chao, delivering the majority decision.