The two groups - one a global militant organization founded by Osama bin Laden and the other a home grown Indian outfit - were found to have joined forces when investigators discovered their roles in the recent Burdwan and Bijnor bombings.
Al Qaeda chief Ayman al-Zawahri announced Sep 4 the forming of its group's wing in the country, by promising in a video posted online the need to spread Islamic rule and "raise the flag of jihad" across the "Indian subcontinent".
With the erstwhile IM now having no presence in India, Al Qaeda looked for a new partner and found it in the shape of SIMI, which has a pan-India network.
"The role of Al Qaeda and SIMI came to light during the Burdwan and Bijnor bomb blasts in the last one month," a top official of the special cell, which deals with all terror-related activities in the national capital and keeps a watch on terrorists outfits, told IANS.
Another official, on condition of anonymity, told IANS: "To impart a big blow in India, Al Qaeda and SIMI had chosen the month of October and their motive was to conduct a series of bombings on Dussehra and Eid-ul-Adha."
However, the accidental blast in Burdwan in West Bengal put paid to the terrorists' bombings plan and they could not carry out any bombings on these occasions, the official added.
"But Diwali (Oct 23) might be on their radar and any Indian city could be targeted by these outfits on this festival," the official said.
Two suspected militants - Shakil Ahmed and Sovan Mandal - were killed and another person Hasan Saheb was injured in the Oct 2 explosion in a house in Khagragarh in Burdwan town. Four people, including two women, have been arrested in the case till now.
The investigative agencies are already on high alert and are not going to take any chances by leaving any loopholes on Diwali, another source, who is privy to intelligence-related information, told IANS.
The official said the Burdwan blast has confirmed Al Qaeda's role and its motive, while the Sep 12 Bijnor blast in Uttar Pradesh has also affirmed SIMI's role.
The recovery of two cartons full of bundles containing 20 match boxes each, a small liquid petroleum gas (LPG) cylinder fitted with wires, two electronic chips and a metal pipe recovered from a house in Bijnor, where the blast took place on Sep 12 morning, is "indicative of the possibility that sleeper cells of the banned SIMI are on revival path", said the official.
SIMI has a modus operandi in which the use of matchstick sulphur is their signature in terror attacks.
"In at least a dozen incidents of terror attacks in southern states, the SIMI signature helped investigators zero in on the accused," the official said.
"The suspects now on the run from Bijnor include Ejazuddin, Mohd Aslam, Zakir Hussain, Mehboob alias Guddu and Amjad, all of whom escaped from the Madhya Pradesh jail a year ago. Their sixth aide is suspected to be Saliq alias Salim, a SIMI operative from Khandwa," he added.
Elaborating on the terror groups, another official told IANS, "If we talk about SIMI's supporting groups, Al Qaeda and IM's names come in the forefront."
"As IM's members appear to have been erased from India, Al Qaeda is the only group which can support SIMI," he said.
"There is no active role of the Indian Mujahideen in India after the arrest of their big Indian operatives in the last few months. Now the only terror group which can unleash mayhem in India is SIMI, which is trying to revive. Al Qaeda is also at the same stage and for this purpose it is backing SIMI, whose members are more acquainted with the topography of Indian states," another official told IANS.
The IM, believed to be a byproduct of SIMI, is banned by the Indian government.
SIMI was formed in Aligarh in 1977 and had thousands of members and offices in almost every district of Madhya Pradesh before it was banned in 2002.
The group is said to believe in fundamentalist Islam and to spread its values. In 2007, the Supreme Court of India described SIMI as a "secessionist movement".
Union Home Minister Rajnath Singh announced the renewal of a five-year ban on SIMI recently as sleeper cells of the outfit revealed their presence in Uttar Pradesh during investigations in the Bijnor bomb blast.