The FBI apparently gave him ample chances to back out so it wasn’t entrapment. Mohamed Osman Mohamud is 19 and will probably spend the rest of his life in prison. Planning violent jihad with someone you met on the net is right up there with middle-aged men thinking it really is a 14 yo girl in that chat room. Dumb. But dumb people are also capable of extreme violence.
The FBI operatives cautioned Mohamud several times about the seriousness of his plan, noting that there would be many people, including children, at the event, and that Mohamud could abandon his plans at any time with no shame.
The FBI did this one right.