The shooting of a Mumbai crime reporter in broad daylight has stunned India's financial capital and brought into sharp focus the seedy underside of the metropolis. Jyotirmoy Dey, 56, wrote extensively on crime, from gang wars to underworld dons. Before his death, the journalist for Mid Day newspaper, had been looking into the city's oil mafia, known to make huge profits from the sale of pilfered petroleum products. The police, who on Monday (June 13) released a sketch of one of the four assailants, said the role of the oil mafia was under investigation. "It (the involvement of the oil mafia) is one of the leads we are looking into," Assistant Commissioner of Police Himanshu Roy told The Straits Times. Criminal gangs dilute higher-priced petrol with subsidised kerosene that they have stolen from tankers and undercut the market with the resulting blend. Media reports say that based on police estimates, the annual turnover of the fuel racket across Maharashtra state, of which Mumbai is the capital, is around 100 million rupees (US$2.2 million). Oil mafia members were also suspected of being behind the murder of a government servant in Malegaon, another city in the state, in January. Deputy collector Yashwant Sonawane, who was burned alive by suspected gang members, had led raids against the local oil mafia. The police investigating Dey's killing are also examining the role of a local senior police officer suspected of threatening the reporterafter he was named as having links with the underworld in one of Dey's reports. Mumbai is known as the financial capital of India with top business honchos conducting business worth billions of rupees out of their plush corporate offices. But the killing of Dey last Saturday is a reminder of the city's underbelly. Dey was one of the leading chroniclers of this side of Mumbai, writing numerous articles on underworld activity and penning two books - Khallas, on underworld operations and Zero Dial, on police informers. Underworld activity in Mumbai was at its peak in the nineties with gangs involved in everything from the drug trade to prostitution to terrorism. But it was reined in by tough police action including the controversial use of police specialist squads, which killed criminals in staged encounters. "It (underworld activity) had not gone away but things were under control. This killing is surprising because gangs (in Mumbai) don't usually target journalists as it brings attention... but there must have been a strong reason," said B. Raman, a former intelligence officer. The Maharashtra state government has put five teams of 80 policemen on the case. It also said it may consider turning investigations over to a federal agency at a later stage. "This killing underlines the increasing threat investigative journalists are being subjected to by powerful political and business interests indulging in illegal acts," said a statement from the Mumbai Press Club, which organised a protest march on Monday. Three journalists including Dey, have been killed in the last six months and more than a dozen attacks recorded all over the country. Mumbai crime reporters probably have one of the most challenging reporting jobs in the country. "Mumbai crime coverage is different from other cities. It is a very delicate balancing act. We are talking of gangs and cops who have links with gangs. There are many layers. And Dey used to be after very high-value extortion crimes," said Mumbai Press Club president Gurbir Singh.