The statute of limitations was put on 'pause' when he left FL. FL still has plenty of time to charge him.
(1) A person commits theft if he or she knowingly obtains or uses, or endeavors to obtain or to use, the property of another with intent to, either temporarily or permanently:
(a) Deprive the other person of a right to the property or a benefit from the property.
(b) Appropriate the property to his or her own use or to the use of any person not entitled to the use of the property.
(2)(c) It is grand theft of the third degree and a felony of the third degree, punishable as provided in s. 775.082, s. 775.083, or s. 775.084, if the property stolen is:
1. Valued at $300 or more, but less than $5,000.
The punishments in 775.082-.083 are 5 years and/or $5000 fine.
Your friend will need to prove that he left FL before the forgeries occurred. Does he have any old leases? Old checks showing his out of state address? Proof of when he closed his FL bank account or opened the new one? When did he get his new driver's license? Also, where were the fraudulently obtained checks deposited/cashed? Were they deposited into someone else's account?
Has he been extradited back to FL? He should talk to a criminal defense atty about whether sending the FL police/prosecutors proof he was out of state might induce them to drop the charges or at least investigate more thoroughly.
He should also have an attorney draft a letter to the temp agency, attaching proof that he was out of state or not working for the agency when the forgeries occurred, and informing the company that he will sue them for libel to recover his costs in defending the criminal charges, and his lost wages if he loses his current job because of the criminal charges. It is to be hoped that this will induce the temp agency to inspect its records more carefully and retract its statements to police.
This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.