A 59-year-old man who sexually assaulted his 12-year-old stepdaughter less than two years after he was released from prison for rape was yesterday given the maximum 20 years' preventive detention.

High Court Judge Aedit Abdullah agreed with prosecutors that the longest imprisonment term possible was warranted to protect the public, especially young girls, from the man's sexual proclivities.

The man, who cannot be named to protect the identity of the victim, was sentenced to 24 years' jail and 24 strokes of the cane in 2001 for raping his 11-year-old niece.

After he was released from prison in 2016, he married a divorcee in January 2017.

The woman knew of his crimes but believed that he had changed and trusted him enough to leave him alone with her daughter from her previous marriage.

However, the man began touching his stepdaughter inappropriately in February 2018. The sexual abuse escalated over almost a year to more intrusive acts.

He usually seized the opportunity to commit the acts when the girl's mother was not looking or was occupied with something else.

He even molested the girl's best friend on two occasions in 2018 when she came over to visit.

The first victim allowed her stepfather to continue taking advantage of her because she was afraid that disclosing the abuse would destroy her mother's happiness.

In January last year, the woman believed that the girl was dating someone and told her she would take her to the hospital to check her virginity.

The girl then revealed the abuse to their neighbour, who told the girl's mother.

The girl's biological father later took her to lodge a police report.

In March, the stepfather pleaded guilty to one count of aggravated sexual assault by penetration and two counts of outraging the modesty of a minor.

Another 12 similar charges were taken into consideration for sentencing.

Prosecutors sought the maximum term of 20 years' preventive detention, a regime for recalcitrant offenders that does not automatically offer the usual one-third remission.

Deputy Public Prosecutor Goh Yi Ling said the man's high risk of re-offending and factors such as his "clear pattern of sexual deviation" underscored the need to impose the lengthiest jail term possible.

Selina Lum