Who could be behind the Mumbai attacks and why?

An interesting Reuters article on who could be behind the Mumbai attacks and why?. One interesting point made in the article:

The Mumbai attacks appear to have been carefully coordinated, well-planned and involved a large number of attackers. A high level of sophistication has also been a hallmark of previous attacks by the Indian Mujahideen.

The Mumbai attacks also focused clearly on tourist targets, including two luxury hotels and a famous cafe....

The tactics -- a military-style assault on soft targets, singling out foreigners, and taking hostages -- are rare and do not fit the usual methods of militant attacks on civilian areas.

However, similar attacks have been carried out before, notably the May 2004 attacks in the eastern Saudi city of Khobar. Gunmen attacked two oil industry installations and a foreign workers' housing complex in the city, taking more than 50 hostages and killing 22 of them. The attackers asked hostages whether they were Christian or Muslim before deciding whom to kill.