Traces of zinc phosphide (rat poison) powder were found in a watermelon, yet no poison containing zinc phosphide has been recovered from Abdullah's residence. (File Photo) The JJ Marg police have been questioning guests and family members who had visited the Dokadia family’s residence between April 22 to April 25 four days prior to the deaths of four members of the family. However, 18 members have been questioned but so far police have not been able to determine the person as well as how the rat poison reached Dokadia family’s home. The investigating officer has been replaced in the case due to the delay in the investigation to nab the culprit and police have recorded statements of more than 20 rat poison vendors. On the night of April 25, Abdullah Dokadia (40), his wife Nasreen Dokadia (35) and daughters Ayesha (16) and Zainab (13) residing in Pydhonie area of south Mumbai had dinner with five other relatives. Around 1.30am, the family of four ate a watermelon and passed away in the next 12 hours.…