Kolkata: The homicide section of Kolkata Police’s Detective Department took over investigation of the Netajinagar elderly couple murder case on Thursday. Several angles have cropped up in the case, but police are still not sure about the motive behind the murders.According to sources, during probe mystery arose over the key of a cupboard which was found intact after the murder. After breaking it open, police found several documents related to bank accounts and fixed deposits. Also Read – Rs 13,000 crore investment to provide 2 lakh jobs: MamataInvestigators suspect that as the elderly couple was issueless, they might have had prepared a will which is yet to be traced. It was also found that the murderers had taken away the mobile phone of Dilip Mukherjee, but did not take the mobile phone of his wife Swapna. The murderers had, however, removed the SIM card from her mobile phone. Police are checking the call list of the deceased couple in order to identify those who were in touch with them. Also Read – Lightning kills 8, injures 16 in stateThough police have already interrogated several persons including a mason who used to reside at the said house on rent, nothing suspicious could be found till Thursday night. However, the investigators are sure that the murderers were known to the Mukherjee family and were close to the elderly couple. On the other hand, police are still in the dark about the motive of the Narendrapur double murder. On Thursday, police questioned the family members of one of the owners of the land and house where the couple, identified as Pradip Biswas and Alpana Biswas, was found murdered. Investigators came to know about a deal which was expected to happen soon over selling the land. It was also found that there might have been some resistance as large traces of blood was found inside the house. After examining the injuries, it was found that it could not have been possible to spread that much blood from the wounds of the deceased persons.