Family members of the boy, Bittu Das, a student of Class X, said they received calls from an "unknown" mobile number at around 8.30 PM yesterday demanding a ransom of Rs 50,000, after their son did not return home.
There were altogether three calls made from that number, they said.
Initially, Bittu's father Nirmal Das, a driver by profession, took the call as a prank and did not pay much heed to it.
"However, when it was around 10 PM and Bittu did not return, they went to the Haridevpur police station and lodged a missing complaint," a senior officer of the Kolkata Police said.
Also Read
Thereafter, Das' family members and their neighbours started looking for Bittu in all possible places in and around the Burrabagan area. They found the boy on the stairs of an abandoned house behind his residence, the officer said.
They rushed Bittu to a hospital at Thakurpukur where he was declared brought dead, he said.
"Bittu was only in his T-shirt. His trousers and slippers were missing. There were injury marks on his lips and around the nose," the IPS officer said.