The investigators were not ruling out this possibility after a comparative analysis of July 13 Mumbai blasts and the explosion outside the High Court revealed that similar components were used in the bombs.
Sources said the analysis showed that in Mumbai blasts, ammonium nitrate was mixed with fuel oil and detonator had traces of PETN while the bomb used in Delhi High Court had PETN as its major component with few traces of ammonium nitrate.
Investigators said PETN is being used mostly by terrorists in Jammu and Kashmir and Indian Mujahideen had earlier used ammonium nitrate for making bombs.
"So now we are looking into the possibility of whether Indian Mujahideen is being helped by some other group," a top police official said.
Meanwhile, investigators have found a switch used in the bomb. Sources said the timer device, if at all used, is yet to be recovered.
Sources said the anti-terror squads of various states were working on the case, but none of them has got any substantive lead in the probe into the Wednesday's blast.
Investigators are not ruling out the possibility of some of the 11 fugitive IM operatives, who were allegedly involved in the 2008 Delhi serial blasts, having played a part in the Wednesday's terror attack.
Another source maintained that unlike this time, in earlier cases there were ample evidence available for the anti-terror squads to make out which IM modules were involved.