Officials said they will question Rana Shaukat Ali, one of the injured admitted to Safdarjung Hospital in Delhi (see his story below), who told authorities he saw two men in his coach get into an altercation with an RPF constable near the Samalkha railway station. Kashmir Singh, the constable, died in the explosion later.

Sources quoted Ali as having told officials he overheard two “suspicious-looking” men as telling the constable that they wanted to go to Ahmedabad. “When they were told the train does not go to Ahmedabad, they said they would get off when it slows down,” sources said, quoting Ali.

Ali apparently saw the two men — they had mufflers on — jump off the train as it slowed before Diwana railway station.

Within minutes, the bombs went off, sources quoted Ali as having said.

Senior RPF officials said there were also inputs that two persons disembarked as soon as the train moved out of Old Delhi. “Many people noticed the two getting off but assumed they had come to see off someone,” a senior RPF official said.

The security establishment is also looking at reports that 4-5 persons conducted a “dry run” at the Old Delhi railway station in January before using a cocktail of ammonium nitrate, kerosene and sulphur to set off explosions on the train last night.

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.