Three robberies within five days across the city and no arrests yet.

Between the first incident in the early hours of Thursday and the third one on Monday evening, the common thread, police suspect, was a person known to the victims passing on information about them to the robbers.

Beyond that the gangs or individuals involved in the three robberies have nothing in common, the police claimed.

Electronic evidence has not helped because either the CCTVs were damaged during the crime or the faces of the robbers were covered. The ones that showed the figures didn’t throw up clear images of the faces, said the police.

Beyond this investigators have not been able to fix whether one group is involved in the three crimes or they were individual acts of crime. If it’s the latter, the police have to depend on their source networks to ascertain the identity of the criminals, senior officers said. That often takes time, the officer said.

“The criminals involved in the robberies at the Central Avenue and the Moore Avenue apartment — the first crime took place on the wee hours of Thursday and the second on Monday evening — don’t appear to be the members of the same gang,” said a senior Kolkata Police officer.

“The style of operation is different. The elderly woman in the Central Avenue house was threatened but not injured. At Moore Avenue, the woman was pushed, hands tied and her mouth was gagged with a vest,” said the officer.

Senior officers who have probed multiple robbery cases across the city over the last few decades said the way members of a gang go about committing a crime often gives away the style of operation of their leaders.

“Some would use thick ropes to tie the victims, others would opt for strong threads (sutli). In some robberies, gang members would slap the victims, use a particular tone and a weapon to threaten and leave a signature while leaving — either eating from the refrigerator, defecating or physically abusing women,” a senior officer of the detective department said.

“In Central Avenue and Moore Avenue, nothing like that happened.”

In Dum Dum Cantonment, a group of seven robbed an elderly couple early on Monday.

“From the way they entered the house, their language and behavior, this seems to be a separate gang,” said a senior officer of the Barrackpore police comissionerate.

"Four gang members had their faces covered with helmets. The faces of the rest aren't clear in the footage," said the officer."

Investigators probing the robbery at the Central Avenue house between February 12 night and the early hours of February 13-said the person who entered the three-story building left behind his gamchha (towel) with which he covered his face while damaging the CCTV outside the room where a 68-year-old woman lived.

"If he had his face covered while leaving the property, CCTV footage from the cameras installed outside the house on Central Avenue would have helped us. We are left with random scanning of grabs based on the suspected time of departure of the individual," said a senior officer who is a part of the probe team. At Moore Avenue, the woman said the attackers appeared to be gig workers and attacked her while she was about to enter her apartments.

"We are scanning the records of history sheeters with similar operation style. Mul- tiple channels have been activated to gather information. Hopefully, we should be able to crack the case soon," said a senior officer of Regent Park police station.