The incident occurred in the suburban Powai area of the city. According to police, four motorcycle-borne men fired at Mr Dey this afternoon. The shooters escaped from the spot, police added.
"Approximately, 9 entry-exit wounds were found which means at least 5 bullets were fired", Vishwas Nagare Patil, Additional CP, Special Branch, Mumbai Police said.
The deceased headed the crime bureau of the publication.
Reacting to the incident, Maharashtra PWD Minister Chhagan Bhujbal told NDTV that he was 'shocked' by the attack. He further added that it appeared to be a handiwork of the underworld.
"The way he was killed shows that it was a well-planned attack...must be an attack by underworld", Mr Bhujbal said.
Mr Dey is considered to be arguably India's best-connected writer on the Mumbai underworld. He spent most of his reporting career bringing out accounts of the goings-on in the Mumbai underworld for several newspapers including the Indian Express and the Hindustan Times.
He is the author of 'Zero Dial: The Dangerous World of Informers' and 'Khallas' - considered a dictionary on the Mumbai underworld.
Mr Dey also wrote extensively about fugitive don Dawood Ibrahim, Chotta Rajan and others. He was reportedly working on a series on Dawood when he was killed today.
j dey died photos, j dey died news, j dey dead photos, mid day news journalist died, mid day news journalist dead, mid day journalist died, Jyotirmoy Dey died, mid day journalist Jyotirmoy Dey dead in mumbai, j dey died in mumbai j dey died photos, j dey mid day journalist