Yau had sexually molested the victim at her home during private tutorials, on three occasions in 1986 and 1987, the prosecution said. The victim, then 12-14 years old, is now 36 and married.

The victim did not disclose the attacks to anyone, but continued to endure the trauma they caused, the prosecution said.

The attacks came to light only after the victim learned Yau had became headmaster at TWGHs Kwan Fong Kai Chi School, a special-needs school in Shek Kip Mei.

Worried that Yau would victimise more girls, the victim sought help from a social worker earlier this year. The case was later reported to the police, Yau was arrested and resigned from the school.

“Imprisonment is almost certain, which is likely to be no less than three months. But the court needs the trauma assessment report on the victim to come up with a fair sentence,” Lin said on Thursday.

Government lawyer Teresa Kam told the court yesterday that the case, for technical reasons, could not be transferred to the District Court despite the severity of the offence. Yau was technically no longer an accused person since he pleaded guilty before the magistrate last month, Kam said.

So his case would have to remain in Magistrate’s Court, where the maximum penalty is less severe, she said.

On its website, TWGHs Kwan Fong Kai Chi School confirmed Yau’s resignation last school term, and mentioned the news about his criminal prosecution. It said the school has held meetings with teachers and and students’ parents to explain the situation.

The school said it had not received any sexual complaints against Yau and dismissed parents’ worries. The school has always had in place measures to protect students from sexual attacks, it said.