Kolkata, Sep 12 (PTI) Kolkata Police on Sunday claimed to have solved the mystery behind the murder of a woman and her teen-aged son after arresting her two relatives who allegedly killed them to get her jewellery that will help them clear their debts, officers said.

Acting on circumstantial evidence, sleuths of Kolkata Police's Detective Department arrested two cousins of Sushmita Mondal for killing her and her son Tomojit Mondal at their residence in Parnasree area of Behala on September 6, Joint Commissioner of Police (Crime) Murlidhar Sharma said.

"Since they are known to Sushmita, she had opened the door to let them in. They stabbed her first. Tomojit was attending online classes in another room. They killed the 13-year-old boy as he had seen them killing his mother," Sharma told reporters.

The two accused, one of whom drives the car of an advocate and the other is a CCTV mechanic, were in financial difficulties, he said.

The IPS officer said they had thought that Mondal had enough jewellery to help them clear their debts.

"They knew the woman's husband would not be at home at that time and she would be alone with her son," he said.

However, probably after the murder, they had realised that the jewellery she had was not enough to repay their loans and the ornaments on her person was found intact, another police officer said.

Sleuths had detained her two cousins, residents of South 24 Parganas district's Maheshtala, on Saturday and following extensive question, they reportedly admitted to the crime.

Bodies of Mondal and her son were found lying in a pool of blood inside their flat by her husband.