The incident took place yesterday, when the accused, who is a retired government employee, found his tenant's 8-year-old daughter alone and lured her to his residence in the same building, where he allegedly forced himself upon her, said police.
Later, when the victim narrated the incident to her mother, they approached the police.
But when a police team went to the residence of the accused, where he lived alone, he was missing.
From preliminary investigation, it emerged that the accused went near the railway track after allegedly sexually assaulting the minor and committed suicide there, police said.
A case under relevant sections of IPC and POCSO Acts was registered in connection with the incident and the girl was counselled by an NGO, police added.