The Anti-Terrorist Squad (ATS) in Mumbai on Monday said forensic reports have revealed the use of RDX, ammonium nitrate and fuel oil in the seven blasts that rocked commuter trains on July 11.
ATS chief KP Raghuvanshi told reporters that traces of explosives found at the blast sites were very small in quantity and forensic experts had taken time to anaylse them.
The assistance of the National Security Guard and the Forensic Science Laboratory in Hyderabad was taken to come to a conclusion, he said.
Stating that investigations are at a critical stage, Raghuvanshi said the blasts were the handiwork of someone "beyond the border" but did not name any organisation.
He denied media reports that two persons had been arrested by security agencies in central India and said he was in touch with the police in Gujarat, Madhya Pradesh and Delhi police.