Excessive gas pressure had led to the blast. The cops arrested the kingpin of the racket, Zubair, a scrap dealer from Daryaganj. The other men managed to escape under cover of darkness. Police said the crooks had managed to steal around 3,000 litres of petrol in the week since they had gained access to the pipeline.

The 150-feet-long, 2.5-feet-wide tunnel ended in a small room where the men had fixed a tap and metal pipe to the petrol line. The metal pipe was connected to a rubber hose through which oil was transferred to a modified tanker with three specially designed barrels. The stolen petrol was sold in the black market, to be likely mixed with kerosene and then retailed to users, including Gramin Sewa vehicles.

According to police, Zubair ran a scrap yard on a rented plot there. Three months ago, when he discovered that the petrol pipeline from Bijwasan to Panipat lay close by, he rented the adjacent plot as well. Zubair disclosed to police that he and his associates dug the tunnel in day and night shifts while keeping the entrance hidden behind scrap. Last week, they managed to reach the pipeline.

Police described the suspects as professionals who were involved in stealing oil earlier too. Shibesh Singh, DCP (Dwarka), told TOI that an FIR has been filed against them. "A special team under SHO (Dwarka north) Jasmohinder Singh has been formed to arrest the men," he added.

Recalling the blast, Rajeev, a resident of Suraj Vihar, said that he and his relatives came out of their homes on hearing the loud noise and informed the police.

"Soon, police dog squads, bomb squads and police and BSF personnel arrived," Rajeev said. "They asked us to keep away from the explosion site. IOC officials came some time later and inspected the tunnel."

Sources say that a major tragedy was averted because another pipeline carrying aviation fuel also lies close to IOC's petrol pipeline. The petrol company's engineers fixed the leaks and the tunnel has being blocked.

The cops plan to question the owner of the plot. In the recent months, police have detected pilferage rackets in Mathura, apart from Uttam Nagar and Mundka in the capital.