CHENNAI: Sexually harassed by her brother-in-law, a 23-year-old final year BCom student stabbed him to death in Telephone Colony, near Madhavaram Milk Colony , on Thursday.

Police said Rekha (name changed) and her mother had moved in with her sister Hema, 28, after their father died a few months ago. They lived with Hema, a staff nurse at a corporation hospital in Madhavaram, her husband Mathew Vinoraj, 32, a realtor with an office in Anna Nagar, and the couple’s eight-year-old son Merlin Joseph in Telephone Colony.

“Mathew used to drink every night and make sexual advances toward Rekha,” Madhavaram inspector K Krishnamoorthy said. “Mathew’s wife and mother-in-law had on several occasions warned him against harassing Rekha but he refused to listen to them.”

Mathew came home on Thursday night and drank till midnight. When he was drunk, he dragged Rekha into a room and locked the door. Hema and Lily heard Rekha cry out for help and pleaded with Mathew to leave her alone but to no avail.

Mathew pinned down Rekha but she managed to free herself and began running around the room in desperation as her brother-in-law chased her. Mathew lost his balance and fell in the mêlée.

Rekha found a large kitchen knife on a shelf and swung the sharp end at Mathew, cutting him on the forehead. Mathew, who had started to pick himself up off the floor, staggered backward and Rekha slit his throat and stabbed him repeatedly till he flopped over, lifeless, in the blood-spattered room.

Meanwhile, Hema and Lily were outside the room, screaming at Mathew to open the door. But Rekha emerged with bloodstained clothes and told them what had happened. She called the Madhavaram police and confessed that she had killed her brother-in-law.

Police rushed to the spot and arrested Rekha. She told them that she had acted in self-defence. In a declaration to the police, her sister Hema corroborated Rekha's version of events and said her sister killed Mathew because he was trying to force himself on her.

Investigators spoke to the family's neighbours and found that Mathew had tried to sexually assault Rekha, who studied in a college in the locality, several times earlier, inspector Krishnamoorthy said. "She appears to have acted in self-defence. That is what she told us and that is what she told her neighbours earlier," he said. "We are questioning her about the harassment by Mathew."

Neighbours informed investigators that Mathew and friends were given to drunken shenanigans and that the girl had told them that she was fed up with him and his behaviour toward her.