Poh Yuan Nie, 57, fronted the racket together with three accomplices, who have all been jailed.

Poh, the former principal of a local tuition centre, had been due to begin a four-year sentence last September, but failed to surrender herself.

She is thought to have fled Singapore.

Police in the city-state issued an arrest warrant for Poh, also known as Pony, last November.

They applied for the Interpol "red notice" the following month and have appealed for information on her whereabouts.

A red notice is a request to law enforcement agencies worldwide to locate and arrest a person pending extradition or similar legal action.

The scam took place across several days in October 2016, during sittings for three tertiary entrance exams.

According to local media, Poh's Zeus Education Centre was engaged to provide tuition to six students - aged 17 to 20 - to help them pass their exams and enter local vocational colleges known as polytechnics.

Poh was paid 6,000 US dollars per student, as well as$1,000 in admission fees - but the money was to be fully refunded if they did not pass.

The students, all Chinese nationals, sat for the papers at different venues while wearing skin colored in ear headphones.

Mobile phones and Bluetooth devices were taped to their bodies by Poh and her accomplices, and carefully concealed under their clothes.

Poh's ex-girlfriend Tan Jia Yan, then aged 30, also sat for the papers as a private candidate. She did so with a camera phone attached to her chest via sticky tape, and hidden beneath her clothes.

Using FaceTime, Tan broadcast a livestream of the papers to Poh, her niece Fiona Poh and an employee Feng Riwen, who were waiting at the tuition centre.

The trio then worked out the answers and fed them to the students via their headphones. "If I heard them clearly, I should keep silent, if not, I should cough," testified one student.

The scheme unravelled when an exam supervisor heard unusual transmission sounds coming from one of the students, who came clean when questioned.

In 2020, Poh, her niece and Feng were convicted of 27 counts of cheating. They were each jailed for between two and four years.

A judge had called on the trio to testify in their defence, but they chose to remain silent. The prosecution argued that an adverse inference should be drawn from this, including the ultimate inference of guilt.

In 2019, Tan was jailed for three years on the same charges. At her sentencing, District Judge Kenneth Yap said that the sanctity of national exams had to be protected.

"The notion that students can buy results by resorting to cheating is offensive. It undermines the principle of meritocracy. It can't be that the rich can procure exam results," he said.