Not proven is a verdict available to a court in Scotland. Under Scots law, a criminal trial may end in one of three verdicts: guilty, not guilty, and not proven. A not proven verdict is an acquittal used when the judge or jury (depending on the kind of trial) does not have enough evidence to convict but still thinks the defendant probably committed the crime.
The not proven verdict is often called the Scottish Verdict or the Scotch Verdict.
The not proven verdict was established in Scottish law by 1728, but scholars dispute its origins. On one account, advanced two hundred years ago by the historians Hume and Arnot, the third and distinctively Scottish verdict was rooted in religious oppression. The Crown persecuted the Covenanters, and popular support for the Covenanters made it impossible to convict them in a jury trial. To pare the power of the jury, the Scottish judges began restricting the jury's role--no longer would the jury announce whether the defendant was "guilty" or "not guilty"; instead it would decide whether specific factual allegations were "proven" or "not proven"; and the judge would then decide whether to convict. In a famous trial in 1728, the story goes, a defense lawyer persuaded the jury to reassert its ancient right of acquitting, of finding a defendant "not guilty." Jurors continued to use both sets of verdicts, but "proven" fell away because it was redundant to "guilty." Some historians, however, such as Ian Douglas Willock, have rejected the traditional account....
In modern use, the not proven verdict suggests a strong possibility of guilt but not enough evidence to convict. A person receiving a not proven verdict is not fined or imprisoned, and is not subject to double jeopardy. The real effect of a not proven verdict is stigma for the acquitted person. The verdict can tarnish a person's reputation, as when socialite Madeleine Smith was charged with murder in nineteenth century Glasgow but acquitted with a not proven verdict.
Some modern commentators have suggested that if a reduction in the number of possible verdicts is desired, it is the 'not guilty' verdict (in the sense of 'innocent') which should be discarded. This is based on the logic that if sufficient evidence exists to convict then 'guilty' is the appropriate verdict. If however insufficient or no evidence exists then the charge against the defendant can not be proved. Therefore the result should be 'not proven'. These are the only two logical and legal conclusions which can be drawn. To declare someone 'innocent' is a moral judgment, not a legal one, and as such is entirely beyond the capacity of a court of law. This suggestion is unlikely to ever be adopted....
The Scottish verdict has not been adopted outside of its home country. Its most famous use outside of Scottish law came when Senator Arlen Specter tried to vote not proven on an article of impeachment of Bill Clinton.