So far the investigations have revealed that the suspects are in direct contact with their counterparts in Pakistan, said highly placed sources.

They added that on the day of the blast, nearly 40 telephone calls were made to Pakistan. These included 24 calls made from two mobile phones. One of the sim-cards reportedly is bought by someone in Amritsar and the other is sold locally. It was revealed that one of the buyers had given a wrong address.

Nineteen calls were made from one mobile phone. Rest of the calls were made from public call offices across the city. In all, 3,500 calls were made abroad on that day from the city.

The police have already begun the verification process of callers especially to Pakistan, from the telephones numbers so far traced by the police. However, it would not be easy to trace the calls made on the mobile phone, the sources added. Meanwhile, the police are yet to stumble upon any definite clue into the blast. The police have managed to trace out the registration number of the scooter in the dickey of which the bomb was placed. The police have sent out parties in the scooter owner's search. The police party is yet to return from Delhi.

Inspector General of Police S.K. Singh, when contacted, said the Central Forensic and Scientific Laboratory is yet to submit report of the chemical analysis. "It is expected in a day or so," he said. The report will determine what kind of explosives were used in the blast.