The official also noted a possibility that Pakistan-based groups such as Lashkar e-Tayyiba or Tehrik-i-Taliban Pakistan could be involved.

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Tahawwur Rana, 52, was convicted in June 2011 of conspiracy to provide material support in the plot against the Morgenavisen Jyllands-Posten newspaper and of providing material support to the Pakistan-based Lashkar-e Tayyiba-terror organization.

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However, U.S. counterterrorism officials say signs point to Lashkar-e-Tayyiba, and they haven't seen anything to rule it out.

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