Don't be too sure. See the 'early information.' My guess is the FBI has additional evidence -- but they'd rather not reveal their source. So they'll probably accept a plea bargain. 'You take (a) and don't go to trial or we will use this at the trial to convict you of (b).' All pretty interesting. It's also possible that if there is Israeli culpability in some form, that Israel will get its arm twisted.
Jordan foreign minister says to speak with Kerry on Israel-Palestinian conflict (Reuters)
from the article: U.S. arrests ex-NASA scientist over bid to spy for Israel