SINGAPORE - To earn fast cash, three teenagers decided to rob sex workers here after one of them recalled watching crime television series Crimewatch which had a segment on a similar offence.

The court heard that Theophileous Jebaraj, 16, John Karan Karunakaran, 18, and a 14-year-old boy were "inspired" to target sex workers as they felt that this was a "safer way of committing robbery".

Court documents did not reveal details about the Crimewatch episode.

The two older teenagers pleaded guilty in court on Friday (June 28) to one count each of committing armed robbery.

The youngest offender, who cannot be named due to his age, was convicted on May 15 but has not been sentenced.

Deputy Public Prosecutor Tay Jia En said that Theophileous was sent to the Singapore Boys' Home on Oct 24, 2017, to serve an 18-month sentence for a separate offence, which was not stated in court documents.

He was allowed to temporarily leave the home on Sept 2 last year but failed to return.

While on the run the next day, he met up with the two other teenagers and they talked about their financial woes. John was on probation at the time for offences which were also not specified in court documents.

The 14-year-old boy suggested stealing mobile phones but Theophileous rejected the idea as he felt that "the returns for stealing were little".

Theophileous then recalled a segment in Crimewatch about robbery cases targeting sex workers and the trio decided to commit a similar offence.

After John conducted an online search, they decided to target two illegal sex workers from China who lived in a rented flat in Woodlands.

They went to the flat at around 11.30pm on Sept 5 last year and a 36-year-old woman invited them in.

Her flatmate led Theophileous into a room where he whipped out a fruit knife, pointed it at her and demanded cash. After searching the room, he took from her $100 in cash.

He left the room soon after and told his accomplices to search for valuables. It was not stated in the court documents if they found any. The three teenagers then fled the scene and the 36-year-old woman made a police report on Sept 9 last year.

On Friday, District Judge May Mesenas called for reports to assess if Theophileous and John were suitable for reformative training. Those sentenced to it would be detained at a reformative training centre where they follow a strict regimen that includes foot drills and counselling.

The case has been adjourned to July 18.

Offenders convicted of armed robbery can be jailed for between three and 14 years, and ordered to receive at least 12 strokes of the cane.