NEW DELHI, February 26: The police have arrested four members of the dreaded `tempo gang' after an encounter in Alipur last night. The gang was allegedly involved in 21 cases of armed robbery and dacoity.The north-west district police received a tip-off last night that the gang would strike at a factory in Jindpur village. The informer also reportedly said that the men would come armed. Barriers were erected and when the police saw the Tata 407, they signalled the driver to stop. The men in the tempo fired two rounds at the police party.The police fired back and managed to overpower four of the men. Two of them, however, fled. The four have been identified as Salim (27) from Khurja, Irfan (25) from Meerut, Farooq (23) from Gautam Budh Nagar and Ompal (21) from Bahadurgarh. The first three were living in Seelampur, while Ompal stayed in Samaipur Badli. The police claim to have recovered four .12 bore and .315 bore country-made revolvers, 21 live cartridges, a .12 bore revolver and two used cartridges.The police say the four are involved in 21 cases of robbery and dacoity: seven in Nangloi, four in Sultanpuri, three in Bawana, two in Samaipur Badli, two in Alipur and three in Ghaziabad. The men had been operating out of Delhi and Ghaziabad over the past 10 months and were into looting factories for cloth and metal, added the police.The modus operandi was simple: First they made a survey of the target factory. One of the gang members would chat up the labourers and find out what could be stolen. Next, the men would hire a Tata 407 tempo. At a pre-determined time, around six to nine of the gang would gather outside the factory. Two of them would scale the boundary wall and overpower the watchman. The others would drive the tempo in and start loading the goods.