As Justice Radack wrote in Texas v Varme:
"An acquittal is an official fact finding that the accused is not guilty of the criminal offense with which he is charged."
Jowitt's Dictionary of English Law:
"The term (acquittal) applies to offences tried on indictment, and means discharge from prosecution upon a verdict of not guilty, or on a successful plea of pardon or of autrefois acquit or autrefois convict. Acquittal is a bar to any subsequent prosecution for the same offence."
Once acquitted, a person cannot be tried again for the same offence.
In Canada, ¶11(h) of the Charter of Rights and Freedoms (published here) is as follows:
"Any person charged with an offence has the right ... if finally acquitted of the offence, not to be tried for it again and, if finally found guilty and punished for the offence, not to be tried or punished for it again...."
This is the double jeopardy rule as set out in the Fifth Amendment (USA).
Some jurisdictions permit re-trying of an acquitted person in the event of new and compelling evidence and for serious offences.
For example, in England, a 2003 Criminal Justice Act, at Part 10, empowers a prosecutor to apply to quash an acquittal "if there is new and compelling evidence against the acquitted person in relation to the qualifying offence".
An acquittal serves as a certification that the person formally accused has not been found guilty.
An acquittal results from the prosecutor not proving the case against the criminal defendant beyond a reasonable doubt.
It may arrive before the defendant even presents his/her defence, by way of a directed verdict.
In 1896, the US Supreme Court adopted these words, in Ball v US (Justice Gray for the Court):
"No person shall be held to answer on a second indictment, for any offence of which he has been acquitted by the jury upon the facts and merits, on a former trial; (and) such acquittal may be pleaded by him in bar of any subsequent prosecution for the same offence, notwithstanding any defect in the form or in the substance of the indictment on which he was acquitted."
- Ball v US, 163 US 662
- Texas Dept. of Public Safety v. Varme, 262 SW 3d 34 (Court of Appeals of Texas at Houston, 2008)