A FBI team joined Delhi Police Special Cell and IB to probe if American citizen Winston Marshall Carmichael had any terror link like US LeT operative David Headley. Official sources said that the FBI officials questioning him and verifying his activities back in the US. <br/> <br/>CISF has detained Marshall after a knife was found in his hand baggage at the Indira Gandhi International airport Delhi on Sunday. <br/> <br/>Investigators are also conducting a chemical examination of the herbal plant "Shilajit" in which Winston Marshall Carmichael had allegedly concealed a knife. <br/> Carmichael, a convert from Christianity to Islam, has a tourist visa to India, Pakistan and Bangladesh.<br/>He had arrived in India in the last week of January and travelled to Pakistan in Samjauta Express where he had attended religious congregations of Tabliq-e-Islam and went<br/>upto Karachi before flying to Dhaka in a Pakistan International Air flight.<br/> <br/>Carmichael later entered India through West Bengal and took a train to the national capital where he was staying in a hotel at Nizamuddin. <br/> <br/>In the meantime, the Delhi Police and security agencies are verifying his places of stay in the national capital and travel from West Bengal. <br/><br/>