The statue of limitations has passed on the crime and he can not be prosecuted.
If the bank that was allegidly robbed was a federally chartered bank, a member of the Federal Reserve, or a bank insured by the FDIC (in other words, almost any bank), then robbing it is a federal offense (18 U.S.C. ? 2113). Thus, the Statute of Limitations would be governed by 18 U.S.C. ? 3032(a), which says "Except as otherwise expressly provided by law, no person shall be prosecuted, tried, or punished for any offense, not capital, unless the indictment is found or the information is instituted within five years next after such offense shall have been committed."
Note that once the defenant is indicted, the statute of limitations clock stops ticking, whether that person is "in custody" or not.
Note also that by robbing a bank, the defendant may be guilty of crimes under state law, which will be subject to a different statute of limitations