The body of a 10-year-old girl, missing since November 5, was found in the early hours of Saturday by the tracks near Vidyavihar railway station in the metropolis, police said.
The girl, who is mentally unwell, had gone missing from Rajiv Gandhi Nagar area, and her parents filed a missing complaint following which teams started tracing her, a Bhandup police station official said.
A man identified as Ajit Kumar Rai was arrested after CCTV footage from the area showed him leaving with the girl on the day she went missing, he said.
"Local residents found Rai in the area on November 8 and brought him to the police. We got a tip-off on the same day about a body lying in the tracks. We found it was of the missing child," he added.
He said further probe into the case is underway and a medical report of the deceased was awaited.