Several persons have been detained for questioning by the Punjab Police following the blast on Sunday at Ludhiana’s Shringaar Cinema — the toll has been revised to six dead and 32 injured — but it is still unclear who was behind the blast. No militant group has owned up so far.

But investigators are looking at the possibility of members of dormant pro-Khalistan groups joining hands with Pakistan-backed terror outfits such as the Jaish-e-Mohammed and Harkat-ul-Jihad-i-Islami to foment trouble in Punjab.

“We had reports that Khalistan Zindabad Force chief Ranjeet Singh Neeta, who has been in Pakistan for many years now, was trying to activate cells in the region. Since Neeta is being protected by the ISI, there is a possibility that he is collaborating with Pakistan-supported jihadi outfits. But as of now, nothing is final. We are looking at all possibilities. This one seems probable though,” said a senior police officer.

Neeta is among the 20 most-wanted India wants Pakistan to hand over.

A NSG team, accompanied by forensic experts, reached Ludhiana this morning to join the probe, especially to examine the material in the bomb.

The police were also awaiting reports from the Patiala forensic laboratory where samples have been to ascertain the kind of explosive used.

Maintaining that the blast was aimed at migrant workers settled in the industrial town of Ludhiana, investigators admitted they were still to make any breakthrough. “The persons that have been picked up for questioning are mainly known anti-social and criminal elements. They may or may not have anything do with the blast,” an officer said, adding that the possibility of RDX being used seemed strong after spot verification.