KOLKATA: In the first honour killing in Kolkata in decades, a 29-year-old youth dragged his sister out on the street and cut off her head with one stroke of the sword in Ayubnagar locality of Nadial, barely 13km from the city centre, on Friday.

Scores of residents looked on in horror as Mehtab Alam walked to a police station with the head in his left hand and the sword in his right, dripping blood all along the way.

At 11am, the duty officer at Nadial police station jumped to his feet in horror as he saw a young man walk in with the macabre exhibits. Before he could find the words to alert his colleagues, Mehtab put the sword and the head on his table, pulled up a chair and told him that he was ready to be arrested for murdering his sister, 22-year-old Nilofar Bibi . He told the duty officer to "seize the head as evidence", say sources.

Even as deputy commissioner-port division Mehboob Rehman rushed to the scene of crime, where Nilofar's headless body lay in a pool of blood, Mehtab told the numbed police officers that he had killed his sister for "running off with a lover and dishonouring the family", say sources. Nilofar was married for eight years and had two children. It was "immoral" for her to live with her former paramour, Firoz Hossain, Mehtab apparently told police.

Firoz escaped because he wasn't home. "I'd have killed him, too," Mehtab told police. He had even attacked Firoz's sister-in-law, Saboo, who tried to save Nilofar. Saboo's right arm is nearly severed and she is battling for life in hospital, said joint commissioner-crime Pallab Kanti Ghosh.

Nilofar married Akbar of Pachura, Rabindranagar, when she was 14. They have a son aged six and a daughter, four. On November 28, she ran away from her in-laws' home, alleging that she was being harassed and tortured by Akbar's brother. On November 30, she disappeared from her paternal home, too.

Nilofar's father lodged a missing person's diary at Nadial police station. In a few days, Mehtab came to know that she was with Firoz, with whom she had an affair before marriage, say police.