While investigators here try to map David Coleman Headleys network in India,it turns out that US investigators had Headley under surveillance a month before the 26/11 attacks in Mumbai. They monitored him for a year before the FBI arrested him at the Chicago airport on October 3 as he planned to leave for Philadelphia en route to Pakistan. Until now,sources said,the US has not passed on any information suggesting that Headley had any links with the Mumbai attacks or that he was aware of the plot. On the other hand,Headleys accomplice,Tahawwur Hussain Rana,possibly came under US surveillance after 26 For,according to immigration records here,Rana was in India for about three weeks in November 2008 and left the country days before 26 Investigators here are looking at this visit to explore any links between Rana and the Mumbai attacks. During his stay,Rana visited five citiesDelhi,Mumbai,Ahmedabad,Pune and Kochi. These were cities that Headley too had visited during his nine trips between 2006 and 2009. In fact,the Kochi visit is said to have got investigators perplexed because the mobile phone Rana was using was not in use there. While it is possible Rana may have used another phone,investigators are still to trace those details. There is no record of Ranas departure from Kochi but a few days later,there is evidence of him surfacing in Mumbai. According to top officials,the bigger concern for the government is to crack the sleeper cells that both Headley and Rana were in touch with to conduct attacks here. While the arrests may have delivered a blow to those plans,the fact remains that trained terror cells were here for this purpose and they have not yet been busted. Interestingly,US had alerted India on a possible attack on the National Defence College about two months ago. They had not specified the source of the information then but it now turns out that this had emerged during surveillance of the two terror accused. Within a week of Headleys arrest,US agencies had,through intelligence channels,informed India about the case around October 9 which was well before it was made public on October 27. Intercepts of communication and email had also been handed over to Indian agencies,said sources. In fact,National Security Advisor M K Narayanan was in US in the last week of October and was given a briefing on the case. Subsequently,a team headed by a senior Intelligence Bureau official was sent to obtain more details but they were not given access to either Headley or Rana. Under US law,such access is only possible after charges have been formally filed and Washington has told New Delhi that this could take about six weeks after which another team will be sent from here to carry out the questioning.