An 18-year-old boy, who worked as a mason at a building in Ekbalpore, was arrested on Friday for allegedly killing his brother, who was four years junior to him.

Mujahid Ansari, 14, was found lying in a pool of blood on Thursday night in a building under construction where he and his father and brother worked as masons.

Police said his father was the first to spot Mujahid, who had been missing since Thursday evening, on the fifth floor of the building. He had puncture marks all over his face. “It appeared that someone had hit his face repeatedly with a sharp weapon,” said an officer of the homicide wing of the detective department.

During questioning, Mujahid’s elder brother Mubarak allegedly kept changing his statement. And that caught the cops attention.

“Mubarak confessed to his crime. Further probe revealed that a wooden plank with nails jutting out was used to hit Mujahid,” said a senior officer of the port division. “We have learned that the brothers had a strained relationship. But the exact trigger of yesterday’s incident is still unclear.”

The police said the family, from Jharkhand, had come to Calcutta to work as labourers.

Mubarak has been charged with murder of his minor brother, a section, if proved before the court, could lead to a maximum punishment of death penalty.