Police suspect Lashkar-e-Tayiba and the banned Students Islamic Movement of India to be behind the serial blasts in the suburban trains of Mumbai on Tuesday evening.
The magnitude of the synchronised blasts have conclusively pointed to the use of RDX by the attackers, official sources said on Wednesday.
The seven synchronised blasts have killed at least 190 people and left another 625 injured.
According to the police, several modules of LeT and SIMI were busted and huge amounts of explosive materials, including RDX, were recovered during raids at various places in Aurangabad, Nasik and Nagpur over the last two months.
During investigations, it also came to light that similar modules of LeT were actively operating in several towns of Maharashtra, besides Hyderabad and Bangalore.