Nepali, a key former aide of Rajan, was killed in Thailand capital, where he had been living under a fictitious name for the past few years, in November last year.
Nepali had allegedly masterminded the killings of advocate Shahid Azmi and Rajan's close associate Farid Tanasha last year. Nepali had parted ways with Rajan in 2005 after which he formed his own gang.
According to the officer, who spoke on condition of anonymity, Nepali was shot dead by two men as he stepped out of the shop of an acquaintance at the City Market in Bangkok.
Sources in the Mumbai police said the assailants closely tracked Nepali's movements before killing him. The police are awaiting the case papers from Bangkok police, which would to be routed through the Ministry of External Affairs.