The Ram Navami procession that was moving down GT Road in Howrah's Shibpur made an unscheduled stop for almost over 25 minutes in front of a gated complex a few metres ahead of the Shibpur police station on Thursday evening, which triggered the violence, a preliminary finding of the CID suggests.

The spot where the procession of several hundreds brandishing swords and daggers and carrying saffron flags stopped is known for its mixed demography in Kazipara.

Those taking part in the procession stopped there and continued to chant slogans and dance to the tune of music from powerful sound boxes mounted on trailers setting the stage for violence to unfurl, investigators have learnt.

"Several residents of the housing complex had stepped out to greet the members of the procession with sherbet, tilak and gulal and this continued for over 25 minutes. The violence erupted amid someone from the procession claiming someone had hurled a stone," said a senior officer.

A special operation group of the CID has been set up to probe into the incident following an order from the state government on Friday. On Saturday, a team of CID officers visited the trouble-hit pocket of Shibpur and clicked pictures of some of the damaged houses, shops and establishments before going on to speak to some of the local residents.

"If the procession hadn't stopped for such a long time, there would have been a lower possibility of a clash," he added.

A source said CCTV footage revealed that the procession stopped near Panchsheel Apartment, a gated complex on GT Road that stands opposite the locality that is predominantly inhabited by minorities.

Located close to the Shibpur police station, several residents of the apartment complex were witness to the violence on Thursday evening, police have learnt.

Footage available with the police has also shown some youths trying to enter the Panchsheel complex and throwing plastic chairs when others managed to close the entrance gate.

"We are in the process of collecting evidence and stitching up information that is available to understand what sparked the violence, how it escalated and whether there was a design in place," said a senior CID officer.

With tension still palpable in the area almost 48 hours since violence rocked the area on Thursday afternoon, some shops opened during daytime with police teams on patrol and members of the armed police carrying out area domination exercises.

Police said that Internet services were being suspended in some pockets for a few hours as a preventive step.

"We will speak to some of the arrested youths separately and find out more about the planning for the Ram Navami procession and its build-up," the officer said.