SINGAPORE - A primary school's administrative employee has pleaded guilty to sexually abusing three brothers studying there.

The 52-year-old started with the eldest boy in 2009, when he was 11. After the boy left the school, the predator, who by then had gained the trust of the family, moved on to his siblings.

The shocking abuse only came to light in March 2013 when the mother received a text message from the man asking to take her second son out. She asked her son about it.

As the boy kept quiet, his younger brother encouraged him to speak up. Eventually, all three boys revealed what had happened to them, and their parents went to the police.

The man, who cannot be named under a court order to protect the identities of the boys, was arrested two days later.

On Thursday (Sept 29), the man, who was the school's operations support assistant, admitted to three counts of committing an indecent act with a child, one count of sexual assault and one count of sexual penetration of a minor.

Another 31 counts will be taken into consideration when he is sentenced at a later date.

Of the 36 charges, seven relate to the eldest brother, 22 to the second and five to the youngest. Two other charges are for possessing obscene and pirated films.

The thin, grey-haired man, who spoke through an interpreter, admitted befriending the eldest boy, then in Primary 5, in 2009. He brought the boy from school and took him out to the zoo and shopping centres.

That year, he performed oral sex on the boy at a HDB staircase landing. He also showed the boy how to do a lewd act but the boy refused to do it.

When the boy went to secondary school, the man moved on to his younger brothers. He bought them shoes and clothes, telling their parents he was following up on their homework.

The parents, who worked long hours, thought he was genuinely concerned for their welfare.

The man paid special attention on to the middle son, perceiving him as more compliant. The boy was abused for three years, suffering the longest ordeal among the three.

In 2012, the man forced him, then 13, to perform oral sex on him in the toilet at a community centre.

The next year, the accused met him and his younger brother, then 12, after school one day and accompanied them back to their home. He abused them, one after the other, on the same bed. No one else was at home at the time.

The boys are now aged 16, 17 and 18 .