Calcutta, July 31 :     It was a repeat of the Noapara killings. But in this case one of the plotters herself was murdered in the bargain. This is the line of investigation that the CID is pursuing in the Oxytown murder case where four members of the Pal family had their throats slit after being drugged. In 1991, Sudipa Pal had hatched a plot with her tutor, with whom she was in love, and killed her entire family in Noapara, North 24-Parganas, by distributing food mixed with poison. The decomposed bodies of the Pal family were found on June 14 with their throats slit. Forensic examination has revealed that they were drugged before being killed. The investigators now believe that Sohini, the elder daughter of the Pal family, was a partner in the crime with her tutor Lakshmi Narayan Chakrabarti with whom she was romantically involved. Sohini was not only aware of the murder plot but was actually a participant in the crime, CID officials believe. The only difference with the Noapara case is that while Sudipa survived, Sohini got eliminated while the plot was being executed. The CID is resting its case on the following evidence and the conclusions drawn from it: A sedative, nitrazepam, was found in the milk, tea cups and in the chira the family members had before dozing off. Investigators argue that it was simply not possible for any outsider to have mixed the sedative in the food. It had to be the job of an insider who had access to the family?s kitchen. Oxytown residents say that the Pal family had no neighbour who was close enough to have access to their kitchen. Therefore, police say, it is almost certain that Sohini mixed the sedative in the food. The next pointer to Sohini?s involvement, CID officials say, lies in the nature of her injuries. While the throats of Sohini?s father, mother and sister had been slit in their sleep, in case of Sohini the post mortem report states that there are clear indications of her first having been ?gagged? and then her throat slit. Though there were also traces of the sedative in her stomach, the quantity was less than that found in the others. ?She may have had a little along with the others, but not enough to knock her out,? stressed an official. Deputy inspector-general, CID, Partha Bhattacharya, said: ?Sohini was the only one of the four to have been gagged to death and then her throat slit. We also have definite clues pinpointing that Sohini was alive even after the other three members of her family had been killed. She was the last one to have been murdered, apparently because a hitch had cropped up at the time of execution of the plot.? The framing of charges against Chakrabarti also clearly indicates that he had committed the crime in collusion with some other persons on ?common interest?. For the tutor, CID officials claim, collusion clearly points to Sohini with whom he was romantically involved. And the ?common interest? was their impending marriage and plans to move into their new home in Behala. But the hurdle was Sohini?s parents who were opposed to their plans. This is the motive that the police is trying to establish for the crime.