Notice how they became aware of his activities….

According to an arrest warrant affidavit written by an FBI special agent, Mohamud was in e-mail communication in August 2009 with a person believed to be involved in terrorist activities. In December, that person was “located in the northwest frontier province of Pakistan,” the affidavit states.

The two communicated regularly, the affidavit states, and “using coded language, they discussed the possibility of Mohamud traveling to Pakistan to prepare for violent jihad.”

They were almost certainly using the Patriot act provision that allows wiretapping of US citizens when the other end of the conversation is overseas. OMG! Wireetapping citizens!