A man who allegedly tried to rape a 27-year-old tourist in her hotel room at Hilton Singapore had his guilty plea set aside yesterday.

This, after he disputed some details in a pre-sentence report which would determine if he is suitable for preventive detention, a prison regime which could see him jailed for up to 20 years.

Among other denials, 54-year-old Isa Ahmad now claims that he did not rob a second female victim of her mobile phone. As a result of Isa disputing the details, Second Principal District Judge Victor Yeo rejected his earlier guilty plea and set aside his conviction.

After the Singaporean pleaded guilty on Oct 23 to one count each of robbery and attempted aggravated rape, the court heard his past convictions, which involved multiple counts of robbery.

For the offences, he was sentenced to eight years of corrective training and 12 strokes of the cane in June 1994.

Corrective training is a prison regime for repeat offenders without the usual one-third remission for good behaviour. The maximum period is 14 years.

After his release, Isa again committed robbery and was last sentenced in October 2002 to 14 years of preventive detention with the maximum 24 strokes of the cane.

This prison regime is only for repeat offenders who are above 30 years old.

He was finally released in 2016, but on March 12, 2017, he allegedly targeted the two women.

According to court documents, he tried to rape the tourist that day, and later robbed a 48-year-old woman at the nearby Tang Plaza of her mobile phone. His pre-trial conference will take place next Tuesday.

Offenders convicted of attempted aggravated rape can be jailed for up to 10 years and caned.

Isa cannot be caned as he is over 50 years old.