Undercover FBI agent was worried suspect in Oregon bomb plot would 'martyr himself early'

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An undercover FBI agent has testified that he didn't initially take a terrorism suspect seriously until the man began to propose specific elements of a car-bomb plot.

The agent, identified only under the pseudonym "Youssef," testified Tuesday at a trial in federal court that he doubted the sincerity of suspect Mohamed Mohamud in initial meetings in early August 2010.

By the end of the month, however, the agent says he was convinced Mohamud was serious about carrying out a terrorism plot.

The agent says he kept close tabs on Mohamud because he was worried Mohamud would "martyr himself early."

Mohamud was the subject of an FBI sting that ended at a Christmas tree-lighting ceremony in November 2010. Prosecutors claim Mohamud tried to detonate a bomb that was a fake provided by the FBI.