This is a question I find interesting due to an experience I'll
The basic answer is that nonunanimous verdicts are allowed in some
states because the U.S. Constitution doesn't require the states to
require that verdicts be unanimous. Although states are required to
have trials by jury in criminal cases, many of the procedures are
determined by the states.
As you know, the right to a trial by jury was recognized in common law
long before there was a United States. In the U.S., the right to a
jury trial became enshrined in two parts of the U.S. Constitution.
Article III, Section 2, Clause 3 provided that all criminal trials
were to be heard by a jury (although a defendant can waive that
right). The Sixth Amendment elaborated further, guaranteeing the
right to "speedy and public trial by
an impartial jury" in the jurisdiction where the crime was committed.
Although it is a long tradition that jury verdicts be unanimous, the
notion of a unanimous verdict was not explicitly mentioned in the
Constitution. However, for decades it was the understood rule that
verdicts were to be unanimous.
It wasn't until the latter half of the 20th century that a move was
made toward allowing nonunanimous verdicts. There were two primary
reasons for this: first, through bribery a defendant could avoid
convicting by "getting to" only a single defendant; and second, a
single recalcitrant jury could prevent a verdict, leading to a costly
But some felt that allowing nonunanimous verdicts was
unconstitutional; the notion of unanimity was seen as implied by the
Constitution and common law, even though not explicitly provided for.
The U.S. Supreme Court ruled on the issue in 1972 in a pair of cases,
Johnson v. Louisiana and Apodaca vs. Oregon; Louisiana allowed 9-3
verdicts in some cases while Oregon allowed 10-2 verdicts. Basically,
the court found that unanimity was not an essential feature of the
criminal justice system.
You can find details (including court citations and excerpts from the
rulings) on these cases in the following articles:
Letting the Supermajority Rule: Nonunanimous Jury Verdicts in Criminal
Improving the Jury System: Nonunanimous Verdicts
The basic reason that a few states have allowed nonunanimous verdicts
(details on which states have are in the above articles) is because
the legislatures there have deemed it to be a good idea; after all,
the high court has indicated it's their decision to make. With regard
to federalism, the argument on one side would be that it's a state
responsibility to set the rule for how juries operate; the argument on
the other side would be that nonuanimous verdicts are so against the
spirit of the Constitution and so violative of personal rights and due
process that they should not be allowed.
My personal viewpoint as to fairness? I can see allowing a verdict
despite the dissent of one juror, at least in minor cases (such as
misdemeanors). It is possible under the current system for one juror
to hold the system up arbitrarily, and that should not be allowed, at
least in minor cases. I am fearful, however, that allowing two
dissents (as in Oregon) or three (as in Louisiana) in criminal cases
could make it too easy to convict someone.
My personal interest in this is that a number of years ago I served on
a jury in a rape trial in Oregon. The jury's vote was 10-2 to
convict. I was one of those two -- I saw plenty of reason to doubt
the defendant's innocence (although he was probably guilty), and the
other dissenting juror believed the guy was innocent. I really
believed (and still do) that an injustice was done, as the prosecution
simply didn't prove its case. In my view, he shouldn't have been
convicted, and he never would have been if a unanimous verdict had
been required. So I have seen how that system works, and in my
experience it didn't work well.
Google search term: "nonunanimous juries"