Even as investigating agencies continue to probe Pak born Lashkar operative David Headley and Tahawur Hassan Rana into their terror links, the Home Secretary Mr. G. K. Pillai said that it will take four to six weeks to complete investigations into the duo's trail in India. He said, the national investigation agency is trying to find out if the two had played any role in the Mumbai terror attack last year or the serial blast between 2006 to 2008. The two men were arrested in Chicago last month in connection with terror plot in US and other places including India .Speaking to media on the sidelines of a function in New Delhi, Mr. Pillai said that Tahawur Hassan Rana had visited Kochi in Kerala and investigations are on to find out about his activities in the city. In reply to a question on a clean chit to film maker Mahesh Bhat's son Rahul, Mr. Pillai said that clean chit has not been given to any one and investigation is still on.<br/>Meanwhile, searches were carried out in cyber cafes and hotels in Central Delhi's Pahar Ganj area in connection with the terror designs of David Headley who is reported to have stayed there in March this year. However, the police is tight lipped about the searches saying that it is a routine exercise.<br/>NIA team is already in Mumbai to probe the activities of Headley and Rana.