A message was received by Kalyan police on Sunday evening about some body parts lying in bushes adjoining the railway track in Titwala area, he said.
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The police rushed to the spot and seized the highly decomposed head and legs, believed to be of a child around 10 to 12 years of age whose gender was yet to be ascertained, the official at Kalyan police station said.
The other body parts were still missing, he said, adding that a gunny bag was also found near the spot.
The official said they suspect that the culprit killed the child, chopped the body into pieces, packed them in the bag and threw it from a running train.
Efforts were on to identify the deceased, he said.
A case was registered under Indian Penal Code Sections 302 (murder) and 201 (causing disappearance of evidence of offence) and a search for the killer was on, he stated.
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