An anti-terrorist squad from Mumbai, led by DIG Paramvir Singh, is reaching Panipat to join the investigations.

In the 7/11 Mumbai train blasts, RDX was used to blow up coaches. The Mumbai team will look for similarities in the two incidents — in both, timer-circuits have been used.

While investigators have no fix yet on who may have been behind the blasts, top government sources said that they were not ruling out the involvement of those opposed to the Indo-Pak peace process.

It’s suspected that four suitcases packed with IEDs, each weighing 20 kg, were placed in the train before it left Delhi. Official sources said that two of the bombs blew up in the general compartment, another was defused later while a fourth was thrown on the tracks by a passenger, a Pakistani national.

While the first and the second IEDs were timed for 11.45 pm and 11.50 pm, the bomb recovered later had been timed for midnight. The recovered suitcase had a steel pipe filled with sulphur, a detonator, a clock timer (used in Mumbai, Delhi and Varanasi) and packed with 14 bottles of ammonium (some say it is potassium) nitrate with kerosene.

This was wrapped in a Hindi newspaper which had an advertisement for a walk-in interview dated January 21.

This, security agencies point out, suggests that the bombs were probably assembled around that date.