In 2003, Khalid Sheikh Mohammed -- who is also a suspected mastermind of the 9/11 attacks on the United States -- was arrested in Pakistan and has confessed to killing Pearl.

Federal agents backed up Mohammed's confession by comparing photos of the veins in his hands and the vein patterns of an assailant in the video of Pearl's killing, according to a report by Georgetown University students and faculty and the Center for Public Integrity.

But Mohammed has not been charged in Pearl's death. According to the report, U.S. officials decided against bringing charges in the Pearl case to avoid complicating Mohammed's prosecution for the 9/11 attacks.

Al Qaeda expert Rohan Gunaratna said Mohammed ordered Pearl's death.

"Daniel Pearl was going in search of the al Qaeda network that was operational in Karachi, and it was at the instruction of Khalid Sheikh Mohammed that Daniel Pearl was killed," Gunaratna said.

Words from his widow

Pearl's death should be a global wake-up call about "a vast and international network of terrorists," his widow said.

"I know Danny has not been defeated" by those who killed him, Mariane Pearl told CNN weeks after her husband's death. "His spirit, his faith and his conviction have not been defeated."

She said governments across the world must take responsibility for fighting terror and citizens should take an active role in considering their countries' foreign policies.

"If people in the world do not realize that they're not immune against this anymore, then nothing will," she said.