When I write posts, I usually try to focus on unsettled areas of law. If the answer can be found just by reading the statute, what do you need me for?
But I have reason to think the answer to the titular question is not universally known. And some attorneys don't know what they don't know, and therefore they have no incentive to track down the answer.
The answer is: sometimes just one, but never more than three.
In a situation where the jurors unanimously found the defendant guilty of the underlining offense, only three jurors must agree on a verdict of "no" in order for the finding to be against the state. Where the jurors were not unanimous on guilt, a situation could arise where only one juror, who had previously found the defendant guilty, could vote "no," and that one juror could defeat the enhancement fact.
ORS 136.785 states in part:
136.785 Burden of proof; effect of finding.
- When an enhancement fact is tried to a jury, any question relating to the enhancement fact shall be submitted to the jury.
- The state has the burden of proving an enhancement fact beyond a reasonable doubt.
- An enhancement fact that is tried to a jury is not proven unless:
- (a) The number of jurors who find that the state has met its burden of proof with regard to the enhancement fact is equal to or greater than the number of jurors that was required to find the defendant guilty of the crime; and
- (b) Of the jurors who find that the state has met its burden of proof, at least the minimum number of jurors required by this subsection to prove an enhancement fact are also jurors who found the defendant guilty of the crime or alternate jurors as provided by ORS 136.773.
In other words, in a 10-2 verdict of guilt, only one juror from the 10 who found the defendant guilty must find for the defendant in order to "acquit." (Okay, "acquit" isn't the right word, but you get the idea.)
This can require great care in both jury instructions and polling, especially if the aggravating factors are tried during the culpability phase. The potential for confusion is great. Not a bad thing, necessarily, as long as you're not the one confused.