The accused then threatened the girl of dire consequences if she reported the matter to anyone, the officer said.
However, the victim later narrated the incident to her relatives following which they approached the police on Saturday and filed a complaint, he said.
A case was registered under the Protection of Children from Sexual Offences (POSCO) Act and other relevant sections of the Indian Penal Code, Deputy Commissioner of Police (Shahdara) Meghna Yadav said.
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The 38-year-old accused has been working as a sweeper in the EDMC-run school for the last three-to-four months. The victim's parents live in Bihar and she stays with her relatives in Shahdara, the DCP said.