"There was blood everywhere," said one bystander. He was referring to a bomb that went off in a crowded market. Two other bombs exploded within minutes of that one which has led authorities to believe it was a terrorist attack by unknown assailants.

BBC:

Three near-simultaneous explosions have shaken India's commercial capital Mumbai (Bombay), police say.

Twenty-one people were killed and 113 injured, said Maharashtra state's Chief Minister, Prithviraj Chavan.

He called the explosions, during Mumbai's busy evening rush-hour, "a co-ordinated attack by terrorists".

One explosion was reported in the Zaveri Bazaar, another in the Opera House business district and a third in Dadar district in the city centre.

Police sources were reported as saying the explosions were caused by home-made bombs.

The attacks are the deadliest in Mumbai since November 2008 when 10 gunmen launched a three-day co-ordinated raid in which 166 people were killed.

The Pakistan-based Lashkar-e-Taiba militant group was responsible for that rampage. This one, however, might hit a little closer to home for India. Bill Roggio:

No group has claimed responsibility for the attack, but the so-called Indian Mujahideen is the prime suspect. India's Intelligence Bureau has previously denied that the Indian Mujahideen exists. Instead the Bureau has claimed the terror group is a creation of the Bangladesh-based Harkat-ul-Jihad-al-Islami, or HUJI-B, an al Qaeda affiliate. HUJI-B created the Indian Mujahideen to confuse investigators and cover the tracks of the Students Islamic Movement of India, or SIMI, which provides logistics for the attacks.

SIMI is a front group for the Harkat-ul-Jihad-al-Islami and Lashkar-e-Taiba inside India. It receives support from Pakistan's Inter-Services Intelligence and is an al Qaeda affiliate. SIMI provides logistical support for attacks in India.

Indeed, the authorities claim that this doesn't appear to have the coordination of a major terrorist assault nor were the bombs very sophisticated. For the time being, there a lot of people who have jumped to the conclusion that Pakistan had a hand in the attack. While not out of the question, this seems more an attack of the homegrown variety.