"We have filed a murder case. We are investigating the matter. I can't say anything more now," said North 24 Parganas police superintendent Tanmay Roy Chowdhury.
The body parts, lying scattered along the tracks, were found early on Saturday.
Demanding the arrest of the culprits, local residents set up road and railway blockades through the day. Police chased protestors with batons when the busy Jessore Road was blockaded.
The BJP has called for a 12-hour strike at Bamongachi area in protest against the killing. A state BJP team led by its chief Rahul Sinha will visit the area Sunday.
"From the balcony, I saw a group of people last night. When they passed by our house, I saw they were beating up and dragging my brother. I informed my father then. We informed the local panchayat member. But nobody came," said Chowdhury's brother.
The locals alleged that Chowdhury had to pay with his life for protesting against illegal liquor dens and gambling rackets operating in the area.