Police have identified from video footage and arrested 12 young men in connection with the rampage at RG Kar Medical College and Hospital past midnight on Wednesday.

Several others have been detained based on suspicion, the police said.

Three suo motu cases of violence, attack on government officials and damage to public property have been started in three separate police stations.

The police said the accused were spotted in videos of the violence and identified with the help of local sources. The accused are from Dum Dum, Belgachhia, Lake Town and Park Circus, the police said.

Investigators, however, did not identify the accused by their names or share their details despite repeated requests from this newspaper.

Many speculated about the political identity of those picked up. A fresh round of rumours swirled in the absence of clarity from the police.

Kolkata Police circulated through their social media handles multiple photographs of the alleged attackers and sought help from common people to identify them. However, there was no formal announcement about the arrests or the arrested persons on Thursday.

As thousands of women walked through the streets of Calcutta at midnight to “reclaim” the roads, a large group of men and women armed with lathis, rods and sharp weapons stormed the RG Kar Medical College and Hospital compound and vandalised the ground floor of the Emergency Building.

At least three departments across two buildings were vandalised.

The unarmed police who were posted in the area were largely outnumbered and were left with no option but to tackle the mob with bare hands.

Several policemen were injured and had to be admitted to hospital.

A senior officer at Lalbazar said the force was given two specific instructions for Wednesday night. “The first was not to engage with the people on the roads at any cost even if there was instigation. And the second was to ensure that all the women who have come on the roads should reach home safe,” said an officer.

None of the cops who were posted at RG Kar Medical College and Hospital were armed with firearms or lathis.

“The apprehension was, that in case of any confrontation or instigation, the police should never strike a student or the common man. Hence they were not even given lathis,” said the officer.

The rioters took advantage of the situation. The mob broke through multiple layers of police barricades and gatecrashed into the Emergency Building to take control of the entire ground floor. Glass partitions were smashed, furniture and lights broken and expensive medical equipment were tossed around. The nurses’ changing room, the police barracks, the emergency ward and the police kiosk outside, were ransacked.

Several doctors who were inside the building ran for their lives and took shelter in the rooms on the upper floors. The seminar hall on the third floor, where the rapeand murder was committed, was undisturbed.

“The place should have been covered by a larger police force. Leaving aside a sudden mob attack, there was also the possibility of an over-enthusiastic crowd of people protesting on the streets walking over to the hospital,” an officer said.

During the court production of the arrested persons, two police officers were allegedly wearing uniform with the name tag of the investigating officer (IO) assigned to the case.

It was later found that one of them was the original IO while the other had allegedly worn the uniform with the IO’s name “by mistake”.

He was asked to remove the uniform and perform his court duty in civvies, sources said.