Calcutta, Jan. 30 :    Calcutta, Jan. 30:  The police were at a loss. Four constables had been shot in front of the American Center and there was not a single lead to follow. The situation was as bad as it gets. But at 4 pm on January 22, luck seemed to swing Calcutta Police's way. An anonymous caller phoned Lalbazar and said he wanted to speak to police commissioner Sujoy Chakraborty. It was urgent, the caller said. He had information on the killing. The caller (who subsequently revealed his identity but the police are not disclosing it) told Chakraborty he was a resident of central Calcutta and had just stepped out for a morning walk when he found a blue Maruti 800 parked in front of his house. 'It somehow seemed strange that a car should be waiting right there,' he told the commissioner. 'There was a middle-aged man sitting inside, looking straight ahead, while a young man waited outside, leaning on the side of the car. I was curious but, nevertheless, I carried on.' Cutting short his walk - 'I was a bit uneasy about the car, so I wanted to figure out what was happening' - the caller returned home at around 7 am. To his surprise, he found a motorcycle had also arrived at the spot. Two men got off the bike, the pillion rider carrying 'something inside a cricket bat cover'. 'I have played cricket and I was in the NCC. I can assure you that it was not a bat inside that cover,' the caller told Chakraborty. 'It had to be something else. What it was, I had no idea at that point of time. It was only later that I figured out what it was.' The witness then proceeded to give Chakraborty a description of the four persons, the car, including its number, and the two-wheeler. He also described the cricket bat cover ('It was either purple or mauve') and the logo on it. He told the police that the two youths on the motorcycle then slipped into the car with their 'bag', while the one waiting outside made off with the motorcycle 'towards Beniapukur'. The car followed. Of the two men on the motorcycle, he said: 'One was fair. He had a moustache and was of medium height; the other was clean shaven and he, too, was fair.' 'This information helped us a great deal,' Chakraborty said. 'We drew the first Identikit picture of the two of them on the basis of the information that my caller provided. In fact, it was sheer providence that he managed to observe the entire proceedings so minutely.' The police commissioner admitted he had no clue about the assailants till the man called up. 'He described in detail what he had seen. It was on the basis of his information that we could piece together what transpired after the shootout.' The caller phoned Chakraborty two more times on January 22. Each time, he provided more information on the killers. 'He realised what he had witnessed after he saw the news on television and understood how important it was for him to reach the information to us,' Chakraborty added. In the next two days, the police got back to him to verify the information received. 'After Zahid was killed in Hazaribagh and his photograph appeared in the newspapers, we got back to the caller to check if he could identify him. He told us this was the pillion rider he had seen last Tuesday,' Chakraborty said.