``Before today's explosion, RDX has surfaced at least thrice in the Punjab-Haryana-Delhi belt during the last one month,'' said DCP (crime) Karnal Singh. ``Though only one RDX related explosion took place in same period,'' he added. Last month, an RDX bomb exploded in a train near Ambala in Punjab. Seven days later, the Delhi Police arrested a man near India Gate and recovered 250 gm of RDX from him. And only yesterday, the Haryana Police made an RDX haul from Panipat.

Today, the EMU train started from Panipat. And the Delhi police suspect that the bomb was planted there. They are, however, also not ruling out the possibilty that someone could have planted the bomb between Panipat and Holambi. Three persons boarded the train at Narela, one station before Holambi. ``It seems that the bomb was meant to explode in Delhi where it would have had maximum effect. But the terrorists got their timing wrong,'' said an official investigating the blast.

Though no group has so far claimed responsibility for the detonation, the Intelligence Bureau suspects Harkat-ul-Mujahideen, formerly Harkat-ul-Ansar -- a Kashmir-based militant group. Reportedly, some members of the group have already infiltrated the Capital. DCP Karnal Singh added: ``For the time being, we are concentrating on Panipat. This place seems to have become a hotspot for terrorists seeking to stock up their RDX suppplies. This RDX eventually ends up in the Capital''.