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Tahawwur Hussain Rana, a Canadian citizen and immigration consultant living in Chicago, is at the centre of terrorism investigations in India and the United States that link him to plots in Europe and America—and to the massacre in Mumbai one year ago that killed more than 160 people. Rana, who co-owns a house in Ottawa where he frequently visits, is currently charged in Chicago for allegedly planning an attack against the Danish newspaper that published cartoons of the Prophet Muhammad. But according to Indian reports citing government sources, he is also suspected of playing a role in the Mumbai attacks, perhaps even scouting targets in the days before the massacre.

It is widely believed that the assault on Mumbai was carried out by the Pakistani Islamist group...