Gopal Tiwari had installed at his home night-vision closed-circuit cameras, police said, expressing the hope to find out from the footage who the Burrabazar don had worked for.

An officer said the cops had discovered three infrared cameras in the Pathuriaghata Street house during a raid early on Friday, which resulted in seizure of arms, ammunition and explosives from the ground floor of the six-storeyed building.

"One of the electronic eyes was mounted above the guard's room on the ground floor. The other two recorded visitors climbing the stairs to the first and second floors. Tiwari's flat is on the second floor," an officer said.

The controls of the cameras, which can capture images even in complete darkness, were in Tiwari's living room.

During the Friday raid, a red glow from the cameras caught the attention of the cops.

"The night-vision infrared cameras glow red in darkness and could be spotted easily. Otherwise, it would have become difficult to spot a CCTV camera in the dark," an officer said.

Recently, a similar night-vision camera installed in an office room of a convent school in Nadia's Ranaghat had captured images of some of the suspects who had broken into the building and gangraped a nun.

The footage from the cameras in the Pathuriaghata building could be seen on a monitor in the living room and was recorded in a hard disk.

Investigators said the hard disk had been sent for forensic examination and is expected to throw up images of people who frequented the building.

"If the footage has not been deleted and the hard disk is not damaged, we are hoping to get vital clues from it," an investigator said.

The cameras installed at Tiwari's home are readily available in the market and can be seen in residential and commercial complexes. Night-vision CCTV cameras have even been installed at some important intersections in the city.

According to Calcutta police, most cameras of the type installed at Tiwari's home store 30 days' footage in hard disks.

Thirty days' footage would cover the events leading to the Calcutta Municipal Corporation elections on April 18, the day on which someone from a gang of Trinamul supporters allegedly backed by Tiwari, a murder convict now out on bail, had fired at a sub-inspector in the Girish Park area.

Several people in the locality Metro spoke to said they had seen Tiwari campaign for the Trinamul Congress in the civic elections.

The recovery of arms and ammunition from his house last week has strengthened the allegation that he was behind the post-poll violence in the area.

"Till now Tiwari's name was cropping up in statements of the other accused. But this is the first lead we have found that would help us nail him directly for the violence," an officer had said after the raid.

Wife questioned

Sleuths from the detective department went to Tiwari's house on Monday and spoke to his wife Kamini. They spent more than an hour asking her about his whereabouts.

"We had information that Tiwari had contacted his family on Sunday. Our visit was related to it," said an officer of the detective department.

"Tiwari did not use the SIM cards that are under our scanner on a single occasion since he went missing. On April 20, two days after the shooting at police officer Jagannath Mandal in the Girish Park area, he had communicated with his aides," the officer said.

Additional reporting by Pronab Mondal