A paedophile, who sexually violated the eight-year-old son of a friend despite the valiant efforts of another boy to protect the victim, pleaded guilty in the High Court yesterday .

The prosecution is seeking at least 12 years of preventive detention for Sanusi Ahmad, 57, a recalcitrant offender who has spent a large part of his life behind bars.

The current offences were committed less than a year after he was released from jail for molesting and threatening a 29-year-old woman with a knife in 2013 after she rejected his sexual advances.

The boy and his mother, a single parent who depended on social welfare, lived at a rental flat with another woman and her son, who was the same age as the victim.

Sanusi was a friend of the victim's mother and would occasionally visit the flat. One day in June 2016, he turned up unannounced, while the women were sleeping in the living room and the boys were playing in the bedroom.

The witness was absorbed in playing mobile games and did not pay attention to what Sanusi was doing in the bedroom until he heard the victim shouting "help me".

When he looked up, the witness saw Sanusi performing a sexual act on the victim.

Shocked, he told the man to stop his disgusting acts. But Sanusi stared at him menacingly and asked the witness to sit on the bed as well.

The witness tried to pull the victim away but was physically blocked by the man. He watched helplessly as Sanusi performed oral sex on the victim, who was begging the man to stop.

Sanusi asked the boys to touch him but they refused. He left after giving the witness $10.

The sexual assault came to light some days later after the victim's mother noticed that Sanusi kept engineering opportunities to be close to her son, even though the boy seemed averse to him.

The victim revealed that Sanusi had touched him inappropriately.

According to a child psychiatrist's report, the victim was shy, spoke with a stutter and has learning difficulties.

Sanusi pleaded guilty to one charge of sexual penetration of a minor. Five other charges, including two for showing a pornographic video to the two boys, were taken into consideration.

Deputy Public Prosecutor Yvonne Poon argued that Sanusi was a menace to society who should be taken out of circulation to protect the public. His list of offences included one where he was sentenced to seven years' preventive detention in 1996 for molesting two 10-year-old boys.

The court called for a report to assess if he was suitable for preventive detention. The case will be heard again on March 13.