Officials said none of the four rape cases had been reported, which bolstered the gang to commit more rapes.
The group used to target rag pickers as garbage used to be deposited at the isolated Shakti Mills Compound, and several women rag pickers are known to segregate the garbage from the location, said the officer.
"Bangali's gang would take advantage of this and target rag pickers," added the officer.
"The cases have not been registered as the victims may have been too scared to report the incident," the officer said.
When contacted, Mumbai police spokesperson DCP Satyanarayan Choudhary refused to comment on whether the police would register FIR's in the earlier cases.