So what it boils down to is 1 no vote from the jury and he's walking.
I think the SCOTUS resolved the hung jury/double jeopardy question in US v Perez.
The discharge of the jury from giving a verdict in a capital case, without the consent of the prisoner, the jury being unable to agree, is not a bar to a subsequent trial for the same offence.
The court is invested with the discretionary authority of discharging the jury from giving any verdict in cases of this nature whenever, in their opinion, there is a manifest necessity for such an act or the ends of public justice would otherwise be defeated.
United States v. Perez - 22 U.S. 579 (1824) :: Justia US Supreme Court Center
This remains the rule in criminal trials.
He could still be retried, but I think given the expense the state will do everything possible to prevent that.
Thank God you're around for the legal mumbo jumbo.