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PORTLAND -- A psychologist testified that the FBI used advanced psychological techniques to lure a teenage terrorism suspect into agreeing to a plan that would have killed thousands.

Elizabeth Cauffman, a defense witness in the trial of Mohamed Mohamud, testified Tuesday that undercover FBI agents rewarded risky behavior and used social pressure to convince Mohamud to attempt to detonate a weapon of mass destruction at Portland's 2010 Christmas tree-lighting.

The bomb was a fake supplied by the FBI.

Background: Portland tree lighting bomb plot

Cauffman says recordings of the agents telling Mohmaud he had a choice of whether to detonate the bomb were actually psychologically-coded messages daring him to back out.

Testimony from Cauffman and a previous psychologist witness are part of the defense's efforts to portray the FBI sting as a complicated manipulation of a teenager.

More: How FBI snared Portland bomb plot suspect

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