According to the report by the Star Tribune, the investigation is into a group of Somali-Americans who allegedly conspired to join terrorists in Syria:

The proceedings, which have been going on all summer, appear to be centered on trying to find out who is behind efforts to convince 20 to 30 people that they should leave Minnesota to fight in the Middle East. That question has stymied federal agents for the last year as they have struggled to build inroads and trust with the Muslim community in the Twin Cities in order to cut off a new pipeline of recruits.

Twitchy will continue to monitor this story for further developments.