PORTLAND, Ore. (CN) - A terrorism consultant and a professor of social psychology gave competing theories on how the alleged "Christmas tree bomber" became radicalized at 19 and then snared by an FBI sting.
Mohamed Mohamud, 21, is charged with attempted use of a weapon of mass destruction: trying to detonate a van full of explosives near a Christmas tree lighting ceremony in downtown Portland in November 2010.
The fake bomb was provided by undercover FBI agents who had built a relationship with Mohamud.
Federal prosecutors claim Mohamud picked the time and place for the attack, and that the agents gave him many opportunities to back out.
But Mohamud's public defenders say he had no way to carry out a terror attack on his own, and that the FBI agents, posing as al-Qaida recruiters, entrapped him.
After more than a week of testimony from FBI agents, prosecutors called their expert witness, Evan Kohlmann, on Friday. His testimony continued on Monday.
Kohlmann, who researches radical Islamist groups on the Internet, has been a consultant to government groups and has testified for the prosecution in numerous terrorism cases in recent years.
During this trial, prosecutors have made much of Mohamud's use of radical jihadi websites and forums, and his articles for Jihad Recollections, an English-language al-Qaeda magazine published online.
Kohlmann testified that radical jihadi groups use the Internet to "spur people into action."
There has been an "explosion of media" online in recent years related to violent jihad, Kohlmann said, through which al-Qaida has been "aggressively looking for Westerners" to recruit.
Kohlmann described a range of forums through which people discuss jihad and other political aspects of Islam.
Some of the "very, very hardcore" forums post propaganda from al-Qaida and related terror groups, Kohlmann said.
Prosecutors have presented evidence that Mohamud maintained an active presence of six such forums.
The jury was shown clips from al-Qaida-produced videos that were found on Mohamud's computer.
While Kohlmann acknowledged that there is nothing wrong with viewing jihadi media, he said that a "passionate interest" in such media is often a "warning sign."
"You can't join al-Qaida if you haven't seen their propaganda," Kohlmann testified.
He said that Mohamud had shown a video to the FBI agents that depicted Osama bin Laden discussing the Sept. 11, 2001, attacks with the alleged "ringleaders," and terrorists talking about the 1998 bombings of U.S. Embassies in East Africa.
After Kohlmann was cross-examined by public defender Steve Wax, the prosecution rested its case.
Monday afternoon, the defense team called its first expert witness, social psychology professor and scholar Dr. Fathali Moghaddam of Georgetown University.
The Iranian-born scholar testified that he has published extensive research about the causes of terrorism and radicalization, and gave the jury some background into social psychology studies.
Moghaddam gave brief summaries of renowned studies by Stanley Milgram and Philip Zimbardo that showed how "under certain conditions, ordinary people can carry out terrible acts."
Zimbardo's research, commonly called "The Stanford Prison Experiment," involved mentally healthy subjects role-playing as prisoners and prison guards. Milgram's experiment had "normal people" administer what they thought were electric shocks to strangers at the request of authority figures.
In the context of the trial, Moghaddam discussed how undercover FBI agents used religious language to imply that Mohamud had a "duty" to be a good Muslim and used subtle tactics to build obedience.
The undercover agents who met with Mohamud repeatedly in the months before his arrest often invoked a "council" overseas that allegedly had selected Mohamud to carry out an attack in the United States.
Moghaddam testified that the concept of a "council" created an "even higher authority" that bound Mohamud to the agents' instructions.
By flattering Mohamud and praising him, the older men who posed as authority figures were able to manipulate the teenager, Moghaddam said.
Prosecutors claim the undercover agents, identified by the pseudonyms Youssef and Hussein, gave Mohamud many opportunities to back out of the plot, but Moghaddam said the agents gave only "artificial outs."
Public defender Steve Wax asked the professor if he noticed a "tag team" dynamic between Youssef and Hussein in their secretly recorded conversations with Mohamud. Moghaddam said he did.
"He hardly gets a chance to say anything," Moghaddam said. He noted that in several instances, an agent will refer to Mohamud's "choice" and then quickly change the subject.
The agents' "constant praise" of Mohamud helped in "building up an obligation" to them, Moghaddam said.
On the Internet's role in radicalizing young Muslims, Moghaddam noted that based on his research, it is "very, very difficult" to predict behavior based on words.
He said that "very large numbers" of Muslims have negative attitudes about the United States, and quite a large number also express support for violence.
He noted that Mohamud had discussed travel plans to Yemen, but had "no specific plans" about terrorist actions before being contacted by the undercover FBI agents.
Read the Top 8
Sign up for the Top 8, a roundup of the day's top stories delivered directly to your inbox Monday through Friday.