The man who abducted the 79-year-old mother of Sheng Siong supermarket chain founder Lim Hock Chee in 2014 and demanded a $20 million ransom will be jailed for life and given three strokes of the cane, after his appeal against conviction was rejected.

Lee Sze Yong, 44, had asked for the death penalty after he was convicted in December last year, saying that he could not bear the thought of "hopeless years ahead". He did not appeal against his sentence.

Yesterday, Lee, who had argued his case before the Court of Appeal without a lawyer, said: "Undoubtedly, I had committed a crime."

Head shaved, wearing a purple prison jumpsuit and holding sheets of paper in his hands, he argued that the question was whether the state of his mind "lies within the language of Section 3 of the Kidnapping Act".

The provision states that an individual who abducts someone with intent to hold that person for ransom faces either the death penalty or life imprisonment with caning.

The former sales executive repeated the argument he had made during his trial - that he was not guilty of kidnap for ransom because he had intended to release Madam Ng Lye Poh by midnight that very day, whether or not the ransom was paid.

But the three-judge court dismissed his argument.

Chief Justice Sundaresh Menon noted that the trial judge did not accept Lee's assertion that he would have released Madam Ng empty-handed when the clock struck 12.

"Even if the appellant did have the intention to release the victim by the end of that fateful day... the offence was complete when he abducted the victim with intent to hold her for ransom."

During his trial last year, Lee admitted that he had been thinking of ways to kidnap rich people in Singapore to clear his debts, which had ballooned to about $200,000.

His first target was billionaire investor Peter Lim's children.

He did research on wealthy people and kept an organiser in which he recorded information on potential targets and the means by which he could execute his plans.

He also bought items such as pepper spray, a taser and masks.

In 2013, he started staking out the Hougang house of the Sheng Siong boss and decided to target Madam Ng after observing her movements.

On the morning of Jan 8, 2014, he approached her at an overhead bridge and asked her in Hokkien if Mr Lim was her son.

After she confirmed that he was, he tricked her into getting into his rented Honda Civic by lying that her son had fallen in his office.

He blindfolded her and phoned Mr Lim, demanding $20 million in $100 and $1,000 notes.

Mr Lim eventually negotiated the sum down to $2 million.

Lee then roped in his former lover, Mr Heng Chen Boon, who was not aware of the plan, to help him swop cars and guard Madam Ng.

When Mr Heng pleaded with him to release her, Lee threatened to expose their sexual history.

After being driven around for 12 hours, Madam Ng was released after her son dropped off a bag with the cash in Sembawang Park.

Lee was arrested in Ang Mo Kio shortly after and led police to the bag of cash, which he had thrown into some bushes at the same park.

Mr Heng, 52, has served a three- year jail term on a reduced charge of helping Lee to abduct Madam Ng.