Can the federal government pick up a nolle prosequi case?

No. But if the crime is both a state and a federal crime, the US attorney can begin their own prosecution for the same crime.

Another View: Disagree with the above answer.

A Nolle Prosequi is no guarantee that the defendant either will not, or can not be re-indicted, whether by the state OR the feds;

" Nolle prosequi is a Latin term meaning "we shall no longer prosecute". It is a declaration made by a prosecutor in a criminal case or by a plaintiff in a civil lawsuit either before or during trial, meaning the case against the defendant is being dropped. The declaration may be made because the charges cannot be proved, the evidence has demonstrated either innocence or a fatal flaw in the prosecution's claim, or the prosecutor no longer thinks the accused is guilty. It is generally made after indictment, but is not a guarantee that the person won't be reindicted."

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