A tea planter's 38-year-old son was murdered at home in Islampur, North Dinajpur district, early on Tuesday.

The attackers, who slit victim Abhijit Tarafdar's throat, also attacked his mother Pratibha as she tried to save her son. She was found with critical injuries caused by sharp weapons.

Abhijit's father Rajen Tarafdar owns a tea plantation in the Tin Mile area near Islampur, said sources.

Around 2.30am, the attackers entered his residence in the Netajipally area of the town. Soon after, police were informed and a team from Islampur police station rushed to the spot.

During the initial investigation, the police detained his wife Deepti and another person. The murder was the fallout of an extramarital affair, cops suspect.

“Some criminals entered the house and killed Abhijit. His mother Pratibha was also attacked. The attackers, however, spared his father Rajen, his wife Deepti and the couple's five-year-old son,” said a source.

Pratibha, speaking from her bed at Islampur subdivisional hospital, said: “I heard some people were moving on the second floor of our house. As I tried to intervene, they attacked me and left."

"However, I couldn’t recognise any of the attackers,” she said.

As she screamed, some tenants of their house rushed to help, she added.

The attackers, she claimed, didn’t break in. “The housekeys were in place. I suspect someone had opened the door for them,” the mother added.

Snehashis Thakur, a tenant who stays on the ground floor, said that initially they had no inkling about the crime.

“Abhijit’s wife called us and said that a thief had entered the house. Later, we learned about the murder,” the tenant said.

Jaspreet Singh, the superintendent of police in Islampur police district, said in the course of the investigation, they found that Deepti had an extramarital affair.

“We have arrested her, and based on her information, a person has been detained from Daspara in the neighbouring Chopra block of the district today (Tuesday). They will be interrogated together. We are scanning CCTV footage of the locality,” said Singh.