The incident happened yesterday when the accused took the five-year-old boy to the terrace of his house where he allegedly had "oral sex" with the child, said a senior police officer.
It is suspected that he carried out the act three-four times with the minor over the last week, he said.
The boy seemed traumatized and his mother somehow got to know about what her child had gone through and informed police, said the officer.
The accused, who has a three-storeyed house, had rented out his premises to the family of the child.
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He allegedly lured the child to the terrace on the pretext of playing with him.
A case under Section 377 (unnatural offences) of IPC and relevant sections of the Protection of Children from Sexual Offences (POCSO) Act has been registered against the accused.
He told police that he had been undergoing treatment for HIV for the last seven-eight years or so.
The child was undergoing counselling.
Police are also investigating whether the accused had targeted other children in the same way.