NEW DELHI: Despite lack of a prior warning or heightened threat assessment of a terror attack, the date of the latest Mumbai attack has focused the attention of security agencies on the hand of the jihadi group Indian Mujahideen (IM), given the Lashkar-linked outfit's penchant for striking on the 13th and 26th days of a month.

The IM, acting in consort and at the behest of the Pakistan-based Lashkar-e-Toiba (LeT), is the likely suspect with its network of sleeper cells and sympathizers. Once again, as has been the case often in the past, a terrorist attack has happened on 13th.

Sustained questioning of arrested IM members, including those who willingly collaborated after being held, has failed to resolve the enigma of the dates even though they add up to compelling evidence.

Consider these events:

* May 13, 2008: Terror hit Jaipur with six serial blasts rocking crowded areas, killing nearly 50.

*July 26, 2008: Ahmedabad hit by a series of 21 blasts that killed 57.

*September 13, 2008: A series of six synchronized blasts in Delhi killed around 30.

*November 26, 2008: 10 LeT terrorists killed almost 187 in the worst ever attack on Mumbai over three days.

*February 13, 2010: A terrorist attack at the German Bakery in Pune left 17 dead.

The dates cannot be a coincidence, and are a strong indicator that IM, whose leaders continue to plan and train in Pakistan, might be the hand behind the mayhem.

Indian agencies have been aware of the importance of these dates, although nobody has yet been able to crack the reason why 13 and 26 are the chosen days. In their investigations over the years, agencies have questioned many IM operatives who have been arrested.

The planning and execution of the blasts also bears the signature of the LeT backed group even though no email claiming responsibility has been reported as yet. The blasts were high intensity and the crowded locale of a neighbourhood like Zaveri Bazaar points to the IM.

Aware of the dates, agencies have stepped up vigilance and paid greater attention to terrorist chatter intercepts around these two days. Despite that, sources said, th

ere was no inkling of any impending terror attack.

This year, there is an added ironic twist to these dates: Indian and Pakistani foreign ministers are expected to sit down for important talks on July 26. There was also buzz on the internet — subsequently found to be incorrect — that Ajmal Kasab's, birthday is on July 13.

Intelligence agencies say IM is part of LeT's so-called “Karachi Project”, which uses fugitive Indian jihadis and run by former Pakistan armymen to keep up the terror pressure on India. This not only keeps India off balance, it also increases the deniability factor for Pakistan because IM operatives by and large are in India. The project, revealed by David Headley to the FBI interrogators, has also been linked to Huji in the past. Headley, for instance, was in close touch with Ilyas Kashmiri of Huji. Headley also said IM leaders, Riaz and Iqbal Bhatkal, were living under the protection of the LeT in Karachi.

All metropolitan cities across the country and coastal areas were immediately put on high alert after the serial blasts. The home ministry asked states to deploy additional security personnel at all crowded public places and directed immigration authorities to step up security checks.

Union home minister P Chidambaram, who held an emergency meeting to take stock of the situation immediately after the blasts, said the Mumbai serial blasts were a “coordinated attack by terrorists”.

Chidambaram said the explosions occurred within minutes of each other from 6.45pm and from this it can be inferred it is a “coordinated attack” by terrorists. Stating about post-blast action, the home minister said the National Security Guard (NSG) hub in Mumbai has been put on standby and that the elite force's 'post-blast' team has also been sent to the financial capital of the country. The Central Forensic Science Laboratory (CFSL) team from both New Delhi and Hyderabad has been sent to Mumbai, he added.

Prime Minister Manmohan, who was also monitoring the developments related to the three explosions, spoke to Chidambaram as also Maharashtra chief minister Prithviraj Chavan.