So far, 10 people, including a leader of a political outfit, have been arrested in connection with the case.
"The meat used to be supplied mainly to the sellers of frozen food items, eateries, departmental stores in the state and its neighbouring areas in Jharkhand, Odisha and Bihar. There are others from these neighbouring states who are involved in the racket," a senior police officer said.
The Kolkata Police, along with its counterparts in the districts of Nadia, South and North 24 Parganas, has chalked out a roadmap to investigate the matter, the officer said.
Asked if the meat was supplied to international markets like Nepal or Bangladesh, he said, "During initial grilling, those who have been arrested have admitted to supplying it to markets in Nepal. But we are not sure about it. Our officers are talking to the Nepal police," he said.
The official said the culprits used to collect the meat of dead animals from different places in the state.
The police today conducted raids at a shop selling chicken in Dakshindari in the Lake Town police station area in connection with their probe into the case.
The police had on Thursday seized 20 tonnes of rotten meat from different locations in the city.
The West Bengal government has directed all police stations in the metropolis and the districts to keep a watch on the sale of meat in their areas, officials said.