Authorities in the Indian city of Mumbai have promised a full investigation after a prominent newspaper crime reporter was killed in a drive-by shooting near his home. Jyotirmoy Dey, who wrote extensively about gangland activities in the country\'s financial and entertainment capital for the daily tabloid Mid-day, was gunned down in broad daylight in a northern suburb on Saturday afternoon. Four gunmen on two motorbikes shot him four times at point-blank range and sped off, police said. Dey, 56, was taken to hospital but was declared dead on arrival. Mumbai Police chief Arup Patnaik said the shooting, which has shocked the city\'s media fraternity, was a professional hit by organised crime gangs. The domestic Press Trust of India news agency quoted an unnamed senior police officer as saying that the so-called \"oil mafia\" may have been behind the killing. \"The journalist had extensively written a number of news reports on the oil mafia, which may have triggered them to eliminate him,\" he added. The \"oil mafia\" are racketeers who steal subsidised kerosene from tankers to dilute higher-priced petrol with it and undercut the market with the resulting blend. In January, a senior civil official in Maharashtra state, of which Mumbai is the capital, was burnt to death after uncovering evidence of the practice. Mid-day said that the reporter, who wrote under the byline \"J Dey\", had covered crime in Mumbai for the last 22 years and was the publication\'s investigations editor. He had previously worked for titles including the Indian Express and the Hindustan Times -- both English-language dailies -- and was the author of two books on Mumbai\'s underworld. Mid-day editor Sachin Kalbag wrote in the newspaper on Sunday that Dey was an honest reporter of great integrity. \"It is evident that Dey was a victim of his fearless journalism,\" he said. But he warned against speculation about the motive of the attack. Journalists in Mumbai are planning a protest march in the city on Monday, calling on the state government for greater protection. They claim that Maharashtra home minister R.R. Patil should resign or be sacked, as Dey had told him recently about alleged links between local police and the underworld but he did nothing. The Mumbai Press Club said Dey\'s death \"underlines the increasing threat investigative journalists are being subjected to by powerful political and business interests indulging in illegal acts\". \"Scores of incidents of journalists being beaten or threatened by politicians and local mafia have been brought to the fore in recent weeks and months,\" it said in a statement. Maharashtra chief minister Prithviraj Chavan has said he was \"extremely disturbed\" to hear of the killing. \"(The) media plays an important role in democracy and efforts to terrorise (them) will be foiled,\" he added, vowing that the killers would face \"stringent action\". \"All steps would be taken to ensure that journalists are able to perform their duty without fear.\" India, the world\'s largest democracy, has a vibrant English and vernacular language media, with journalists enjoying a high reputation among readers and the authorities. Attempts to stifle free speech and attacks on journalists are relatively rare. The Committee to Protect Journalists said that 27 journalists have been killed in India since 1992. Most victims were print reporters covering politics, business and corruption. In November 2008, a correspondent for the Hindi-language daily Hindustan who wrote about crime and corruption was shot dead by three men on motorbikes in the northern state of Bihar.