Builder Vinod Asrani (55), who had been out on bail on medical grounds since 2012, was undergoing treatment for liver ailment at a private hospital in central Mumbai's Parel. He died in the wee hours on Friday, said a crime branch officer.
Asrani's family was planning a liver transplant for him in Singapore.
"Asrani was a key conspirator in the case. However, his death would not cause much effect on the matter," said the officer.
Jyotirmoy Dey (56), working with the city-based English tabloid Mid-Day, was shot dead by four motorcycle-borne assailants in suburban Powai in Mumbai on June 11, 2011. Dey was shot from close range at the behest of Rajan and a total of five bullets entered his body.
A month after the killing, the Mumbai Police Crime Branch had arrested Asrani alias Vinod Chembur.
Asrani was alleged to have helped the shooters identify Dey by arranging a meeting with the latter in a restaurant in Chembur area. He was also suspected to have provided assailants the whereabouts of Dey.
Other accused arrested in the case were -- Rohee Thangappan Joseph alias Satish Kalya, Abhijeet Shinde, Arun Dake, Sachin Gaikwad, Anil Waghmode, Nilesh Shendge, Mangesh Agawane, Paulson Joseph, Deepak Sisodia and Jigna Vora.
Currently, Sisodia, Joseph and Vora are out on bail.
Two accused -- Chhota Rajan and his aide N Bisht -- are still wanted in the case, police said.
The trial of the case is yet to begin.