They didn't bother to go to all that hassle. The US Attorney (supported by a federal judge) just asserted federal jurisdiction and moved the case to federal court where it was promptly dismissed with prejudice, so the case couldn't be re-filed.
Just so. But the possibility of further state action in Idaho against US Marshall Degan's widow Karen Degan of Quincy, Mass. for conspiring with Horiuchi to murder Mrs Weaver remains a possibility.
And, since such a conspiracy against the civil rights of Mrs. Weaver remains a federal crime which carries the death penalty, there's no statute of limitations to prevent such a federal action against Horiuchi in the event Karen Dugan would care to testify against him to see possible charges against her lessened.
Of course, Horiuchi may see fit to murder her to prevent that from happening. After all, he's shot one unarmed woman to death already, and he has access to the equipment to do so from H-S Precision.