Agartala, Oct. 6: Police last night arrested brothers Dipjay, 28, and Bitanjay Saha, 26, for killing their mother Shanta Saha, 55, on August 17.

The duo said they had hired two contract killers, Ranada Prasad Roy, 30, and Krishna Dey, 29, to pull off the killing. All four were produced in court and remanded in four days' police custody.

Shanta Saha, wife of police-engineer Dipak Saha, 59, was a resident of government quarters in posh Shyamali Bazar area in northern Agartala. She was stabbed to death.

The officer-in-charge of GB police outpost, Himadri Sarkar, officer-in-charge of capital complex police station Panna Sen and deputy superintendent of police Sanjay Biswas rushed to the spot and sent the body for post-mortem in G.B. Hospital.

The police failed to recover the murder weapon and found no explanation as to why even the pet dog in the house was silent during the murder.

Shanta's husband Dipak also failed to provide any clue.

The case was then handed over to the CID, headed by inspector Partha Sarathi Paul. After investigating for more than a month, the CID team arrested Dipjay and Bitanjay and the two contract killers Ranada and Krishna.

"The motive behind the murder was very bizarre. Shanta was opposed to the immoral activities of her sons. Elder son Dipjay had a relationship with a cousin and used to bring her home often. Even after his marriage he ignored his wife and carried on his affair," Paul said.

Bitanjay was involved in a sex racket and used to produce films by bringing girls home to shoot them. "Santa objected to this. Finally, the brothers decided to have their mother killed," Paul said.

Describing the murder as the "most bizarre crime", Paul said he was hopeful of proving the case in the trial court and get conviction for the four accused. "We have collected evidence and now in the course of police remand we will also find out the murder weapon. Though court verdicts cannot be predicted we are hopeful of conviction of the culprits," Paul said.