Boston Marathon

Minnesota terror case shows challenge of predicting attacks

After Tnuza Jamal Hassan was stopped from flying to Afghanistan last September, she allegedly told FBI agents that she wanted to join al-Qaida and marry a fighter, and that she might even wear a suicide belt.

She also said she was angry at U.S. military actions overseas and admitted that she tried to encourage others to "join the jihad in fighting," but she said she had no intention of carrying out an attack on U.S. soil, according to prosecutors. Despite her alleged admissions, she was allowed to go free.

Four months later, the 19-year-old was arrested for allegedly setting small fires on her former college campus in St. Paul in what prosecutors say was a...

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