Yemeni and U.S. authorities believe Anwar al-Awlaki, a radical al-Qaida-linked cleric, played a role in a number of terrorist attacks. Here is a look at the major incidents.

September 2001: U.S. authorities conduct a series of interviews with Awlaki in the aftermath of the September 11th U.S. terror attacks for his alleged dealings with suspects linked to the plot. However, no criminal charges were filed against him.

August 2006: Awlaki is among a group of five suspects arrested in Yemen for the suspected kidnapping of a Shi'ite Muslim teenager who was held for ransom.

November 2009: U.S. Army Major Nidal Malik Hasan is accused of carrying out a shooting spree that killed 13 people at a U.S. military base. Authorities say Awlaki was a spiritual adviser to Hasan.

December 2009: Nigerian Umar Farouk Abdulmutallab is arrested for trying to blow up a plane as it was approaching the U.S. city of Detroit. Authorities believe Abdulmutallab studied under Awlaki.

November 2010: A French oil industry worker is killed in Yemen. Yemeni authorities believe Awlaki had contacts with suspects arrested for the death. He is later charged with “inciting violence against foreigners.”