What is reasonable doubt?

Why is it necessary for a jury to be unanimous in order for a defendant to be acquitted?

If "we are asking jurors to decide a person's fate based on imperfect information," then should every criminal defendant be acquitted on grounds that imperfect information necessarily generates a reasonable doubt? -- Comment from Randy, Does social media threaten the jury system?

Isn't the very fact that six, or twelve, jurors can't come to an agreement that a person is guilty evidence of reasonable doubt? After all, the burden of proof in a criminal case is on the state, not the defendant. If the state can't convince a panel of citizens in the courtroom that the defendant did something bad, why should the defendant have to go through the time and expense of another trial?

Scott Greenfield at Simple Justice touched on this topic back in September:

In Oregon (anywhere else?), a verdict of 9 for conviction is apparently sufficient to convict, whereas it's a hung jury elsewhere.  Not having tried a case in Oregon, this came as news to me.  Shocking news.  Of a twelve person jury, the fact that one of four jurors found that the evidence failed to prove guilt beyond a reasonable doubt means nothing.  Close enough for government work.  And a conviction.  Next case. 

* In the State of Oregon it takes 10 jurors to convict of any crime short of murder; it takes 11 to convict for murder. A comment to the post pointed out that Johnson v. Louisiana spoke to 9-3 verdicts.

Still, the question remains why the State of Oregon finds a non-unanimous jury verdict acceptable to convict.  Putting aside its rejection of the historical common law understanding that a jury verdict be unanimous for conviction, it seems incomprehensible that a state would believe the rejection of a quarter of a jury that the evidence proved guilt beyond a reasonable doubt to be an acceptable, no less good, idea.  It may be my bias, but it strikes me as barbaric.

In Johnson v. Louisiana, the U.S. Supreme Court held that the Sixth Amendment did not require unanimous jury verdicts in state criminal trials. The Court found that it was perfectly logical for a man to be convicted of a crime if 75% of the jurors thought he was guilty. The very notion is absurd on its face.

How many of us would trust a doctor if he were only 75% certain of his diagnosis? But that's enough certainty in Louisiana to lock someone up in the penitentiary in Angola.

But back to the original question -- what interest is served by ordering a mistrial whenever the jury is hung? We are all considered innocent unless, and until, proven otherwise beyond a reasonable doubt. If the jury cannot all agree that the defendant is guilty as charged, then the state has failed to prove its case beyond all reasonable doubt. That logically means the defendant is not guilty and should be allowed to go about his or her business. Why should the state get another bite at the apple?

Of course logic and law don't always go together.