South Indian Mujahideen (SIM), a hitherto unknown separate module of the Indian Mujahideen, is now suspected to be behind the twin blasts on the Bangalore-Guwahati Express at Chennai Central on May 1, according to investigators.

Although initially the Indian Mujahideen was thought to be directly involved in the blasts, the police are currently investigating if the person they are looking for, Abubacker Siddique, had formed an independent self-styled South Indian Mujahideen. The operatives behind the train explosions are believed to be home-grown Islamist terrorists.

While the blasts are seen as retaliation for the recent arrests of secret operatives in Chennai, whether they are linked to a larger transnational plot remains unclear.

Siddique, the police say, is known for precision killing, aiming only specific targets in Hindutva outfits. After sustained interrogation of Islamist extremists already under arrest, Panna Ismail, Bilal Malik and Police Fakrudeen, investigators believe that he might have been roped in to plan the blasts for triggering panic, and not claiming lives.

The low-intensity explosives placed in the train were facing the floor so as to minimise the impact of the blasts. They were triggered by a timer and not a remote control. Had the train been on time, the explosives would have gone off at Sullurpet in Nellore district of Andhra Pradesh, where the BJP’s prime ministerial candidate, Narendra Modi, was to speak at an election rally in the evening in Nellore.

Ismail, Malik and Fakrudeen were arrested in the Puthur operation on October 5, 2013 in connection with a series of communal murders in Vellore, Salem and Madurai and the planting of a pipe bomb on the Rath Yatra route of the BJP leader L.K. Advani.

Going by the “signature of the blast” (the remnants and pattern of explosion), the police have identified similarities with the blasts in Patna.