"We have invoked MCOCA against all the accused in the case," said Joint Police Commissioner (Crime) Himanshu Roy.
According to police, MCOCA provisions can be applied if at least two members of an organised crime gang have at least two charge-sheets registered against them.
Those arrested in the case include Vinod Asrani alias Vinod Chembur, a bookie who allegedly helped the shooters identify Dey. Asrani was arrested on July 3 and a local court on Thursday had extended his police custody till July 13.
Last week, the police arrested gunman Rohee Thangappan Joseph alias Satish Kalya (34) and his associates Abhijeet Shinde (28), Arun Dake (27), Sachin Gaikwad (27), Anil Waghmode (35), Nilesh Shendge (34) and Mangesh Agawane(25) in connection with Dey's murder.
Dey (56), working with the Mumbai-based English tabloid Mid-Day, was shot dead by four motorcycle-borne assailants in suburban Powai on June 11.
The police had claimed that the journalist was eliminated at the behest of gangster Chhota Rajan, who paid Rs 5 lakh to the accused. However, they said the motive behind the killing was not yet clear.