An interior designer who robbed three Chinese nationals in two separate cases was given 15 years' jail and the maximum 24 strokes of the cane yesterday.

Tan Choon Keap, 34, had tied up all his victims and even asked one to perform oral sex on him. He made the other two strip and took photos of them, threatening to upload them if they told the police.

Tan, who pleaded guilty earlier to five of 13 charges, had called a 25-year-old prostitute on Oct 24, 2013, to book her services. He turned up at her flat close to midnight wearing military fatigues and a helmet to hide his identity.

He robbed her of $1,950 at knifepoint after taping her mouth and tying her hands with cable ties.

After she performed oral sex on him, he tied her up and took two cellphones of hers worth $1,798.

Tan reoffended more than a year later while out on bail.

On Nov 3 last year, he went to the flat of a 29-year-old stall assistant and part-time masseuse, wearing a black cap and a surgical mask.

During the massage, he asked her for sex but she refused. She only agreed to remove her top if he did not touch her.

He later held a knife to her neck, pushed her to the bed and sat on top of her. He gagged her and robbed her of $4,000.

He tied her wrists and ankles and blindfolded her while ransacking her room. He pulled down her panties and took photos of her with his cellphone. He then molested her.

The victim's co-tenant, a 21-year-old student, was also relieved of $4,000. Tan also tied her up and blindfolded her. He found another $10,000 and took it.

He subsequently got the the older woman to cut the younger woman's T-shirt and pull her shorts down to her ankle area, exposing her private parts.

After telling the 29-year-old to remove her clothes, Tan made the two gesture a V sign with their hands and took their photos with his mobile phone.

He was arrested two days later at the Resorts World Sentosa casino.

District Judge Toh Yung Cheong noted the high level of harm and property loss caused to the victims. He said it was clear the offences were planned and methodically carried out.