More Terror on the Tracks; Investigators say two jihadist groups, including a homegrown terrorist organization, are behind the Mumbai bombings.

Byline: Sudip Mazumdar, Zahid Hussain and Ron Moreau

They seem to have drawn little notice as they squeezed aboard the packed first-class carriages. Most passengers were concentrating on getting home from a long, rainy Tuesday at the office in India's financial center, Mumbai. The men placed their duffel bags and metal lunchboxes on the overhead luggage racks, and then, apparently, pushed their way off again, unnoticed--until 6:24 p.m., when the explosions began. Within 11 minutes, bombs had ripped through seven suburb-bound commuter trains on the same rail line. The blasts left 197 passengers and crew dead or dying and 800 others injured.

Police investigators are convinced they know who was behind the Madrid-style bombings. Only two terrorist organizations in the region have the skills and resources for such a massive, coordinated attack--and this, police believe, was a joint operation by both networks. One alleged partner is Lashkar-i-Taiba, a Kashmiri separatist group that has been outlawed since 2002 in Pakistan, the country where it began 16 years ago. The other group is the banned Students Islamic Movement of India (SIMI), a homegrown jihadist outfit that is spreading rapidly among disaffected young Muslims across much of India. Both groups are denying any involvement, but police say evidence against them is piling up.

The authorities released photos of three bearded young men in connection with the attacks. Police said one of the men was the fugitive ringleader of a dozen alleged SIMI operatives who were arrested two months ago in Aurangabad, some 350 kilometers east of Mumbai. In the course of that sweep, police seized dozens of AK-47 automatic rifles, crates of ammunition and more than 45 kilograms of RDX, a military-grade explosive. The arrests had resulted from an investigation that began earlier this year after cops apprehended a pair of suspected Lashkar operatives getting off a train in downtown Mumbai. Police said the two men were found with one kilogram of RDX.

The two organizations are united by the same wild-eyed cause: bringing the entire Subcontinent back under Muslim rule for the first time since ...