On the blood-soaked floor of Plot No. 335, where the police said a raging gun battle had taken place in the early hours of Thursday, lay a red, black and white checked shirt. It was supposed to be clinching evidence. One of the five suspects, Vinod Kumar, was seen wearing a similar shirt in the CCTV footage that was released by the police on Wednesday.

But since doubts remain, what would truly establish the veracity of the police version, or prove to be its downfall, is the invisible forensic evidence that lay scattered on the scene. Reporters who reached the spot soon after the incident were cordoned off by a posse of policemen about a kilometre away from the apartment till 5.30 a.m.

In the tiny 300 sq. ft apartments that dot the narrow lanes of the Housing Board Colony, most people were sleeping, unaware of the storm gathering outside. The first official response came at 3.45 a.m., when Joint Commissioner of Police Shanmugarajeshwaran stepped past the barricade and said, “An incident had happened around 1 a.m. It lasted for about 10 minutes.”

At the break of dawn, access was granted to the crime scene, but entering the apartment was forbidden. Policemen are supposed to have fired their first rounds through the two windows and it had left a couple of bullet marks on the blue walls.

Accounting for all the bullets and the guns from which they were fired from is the first step in a forensic investigation, said P. Chandra Sekharan, former Director of Tamil Nadu's Forensic Sciences Department. “Each bullet will have a unique pattern of ‘striations' from which one can determine which gun was used. Even the dead bodies would have tell-tale signs. The nature of the wound can tell a lot about the range from which a shot was fired.”

One pressing question that needs to be answered, he says, is if the police's initial claim of the use of toy guns in the robbery was true. “How come seven real guns were recovered from the scene?”

“A proper investigation must be conducted at least to establish the honesty of the cops,” Mr. Sekharan said. “The public should be convinced that what was done was right. It is necessary in a democratic system.”

Judicial probe on

The XIVth Metropolitan Magistrate Geeta Rani visited the scene of crime around 3.30 in the afternoon and spent nearly three hours at the spot. Bullet marks were found in over 10 places.

Deputy Commissioner (special officer–bank robbery cases) R. Sudhakar, who led the police team during Thursday's encounter, lodged a formal complaint at the Velachery police station in the evening. A case has been registered under Section 176 of the CrPC, Sections 144, 147, 148, 307, 332 and 506 (2) of the IPC, and Sections 27 and 28 of the Arms Act.

Deputy Commissioner of Police (T. Nagar) Ashok Kumar is the investigating officer for the case.