None Dare Call It Bullshit

But my guy's gonna say it ain't so.  That's reasonable doubt, so I can't be guilty.  Ain't taking no deal.

We've all heard that from our clients.  And then we've watched them hauled off to the pokey because, well, as I've said repeatedly, trials are about proof and proof is whatever the jury believes.  And the jury tends to believe the cops and the alleged victims rather than, say, the defendant's mother or best friend.
But there is this thing about reasonable doubt.  Not just any old doubt.  Reasonable doubt.  And the proof is supposed to be beyond it.
I've been reading (slogging, might be a better word) through the transcript of a capital trial, but really, it could be any trial, civil or criminal.  There are expert witnesses on both sides.  Each is highly credentialed.  And each is determined by the court to be an expert in the same field.*
Each looks at the same evidence.  Defense expert says A.  State expert looks at the same stuff and says not A.
The jury goes back to deliberate.
Guilty or not guilty?
The outcome rests on whether it's A or not A.
The jury has been told it can believe all, some, or none of what any witness has to say.  But it cannot find the defendant guilty unless the state proves guilt beyond a reasonable doubt.  That is, the jury must be convinced, beyond a reasonable doubt, that the state's witness expert is right, that not A.
Here are the three possibilities:

1. One expert is incompetent.
2. One expert is a liar.
3. Experts disagree.

Let's consider those in turn.  
Incompetence
Both experts have credentials, as they say, up the wazoo.  Degrees, affiliations, experience.  Neither side disputed the expertise of the witness on the other side.  And the judge, the authority in the courtroom made specific findings, aloud and on the record in front of the jurors, that each is in fact an expert.
Have the jurors any basis on which to believe one incompetent?
No.  A juror who thought one or the other expert incompetent wouldn't be following her oath.
Lies
Sure, could be.  Witnesses lie under oath all the time.
Cops do it so much there's even a term for it.  It's called testilying.
Now, there are experts and experts.  Some really are whores who'll say whatever they're paid to say.  But there aren't many of them and they don't last long because, frankly, it's obvious.  They're charlatans and mountebanks and everyone can see it.  Competent lawyers don't use them because they won't help.
And serious experts, they don't want to damage their reputation by selling it to the highest bidder.
Disagreement
These two guy looked at the same stuff and just interpreted it differently.  They have specialized training the jury doesn't have.  Education, affiliations, experience.  One says it's flu the other says pneumonia.  One says the widget was badly manufactured, and here's why.  The other says the widget was just fine until the frazmut smashed into it, and here's how I can tell.
Maybe that mushroom is poisonous.  Maybe not.
Maybe global warming.  Then again, maybe it's just getting hotter.

Anecdote

Some years ago, I sat on a jury in a civil case.  The issue, the only issue, was whether the fact that the plaintiff was in more pain after the accident than before was a function of the accident or a coincidentally timed consequence of an earlier injury. 

There were opposing experts.  One we concluded was a whore.  The other admitted cheating the defendant.  One might have been right.  I suppose one has to have been right, in the same way that a stopped clock is right twice a day.  I mean, their positions were X and not X.  So sure, however dishonestly they came to their conclusions, one was right.  It's just that there was no way to tell which one.

Except, she was in more pain after the accident than before.  With no reason to believe the expert who said coincidence, the likelihood was that the accident caused the pain.  Accidents, after all, will do that.

Here's the thing, though.  Civil cases are decided by a preponderance of the evidence.  More probable than not.  She didn't have to prove beyond a reasonable doubt that the accident did it.  If she'd had to prove that, we'd have voted against her. 

End of Anecdote

OK, here's the point.

We look to experts because jurors aren't competent to answer the question.  Is it cancer or a calcium deposit?  Damned if I know.  The jurors really can't tell, either.

Yet they have the job of deciding whether it's proved beyond a reasonable doubt.  When the oncologists disagree.

In an honest system, we'd acknowledge that the state simply hasn't proved it unless one of the experts is believed, beyond a reasonable doubt, to be flat out lying.

Not wrong.

Crooked.

And we'd ask the jury to make a special finding.  If they didn't say 

Fucking asshole lying sack of shit,

then it would have to be Not guilty.  No matter what they decided.

Our legal system doesn't live in that world.  We ask jurors to decide whether the skull fracture was caused by a bat or an auto accident, whether the accused has mental retardation, whether the guy will be dangerous in the future, whether the baby was dropped or thrown. Whether the DNA was his or not.

And, and here's the bottom line.

They can't.  

And yet we send men to death row because of what they say.

In their ignorance.

-----------------
*For any non-lawyers reading this, that's a standard thing.  The lawyers put forth the purported expert's credentials in order to show that the person is, in fact, an expert and asks the judge to make that finding which allows the witness to offer opinions within her field of expertise.