Historical Notes on Clause 6: Procedure in the Ecclesiastical Court - Proof and Jury

Laici non debent accusari nisi per certos et legales accusatores et testes in praesentia episcopi, ita quod archidia conus non perdat jus suum, nee quicquam quod inde habere debeat. Et si tales fuerint qui culpantur, quod non velit vel non audeat aliquis eos accusare, vicecomes requisitus ab episcopo faciet jurare duodecim legales homines de visneto, sen de villa, coram episcopo, quod inde veritatem secundum conscientiam suam manifestabunt.

Lay persons ought not to be prosecuted in the bishop's court except by reliable and lawful accusers and witnesses. But in order that the archdeacon does not lose his right to judge on anything which he ought to do there, and if there be any lay persons who are deemed culpable, but against whom no one wishes or dares to bring an accusation, let the sheriff, at the request of the bishop, cause twelve lawful men from the neighborhood or the manor to take an oath before the bishop that they will examine the truth of the matter according to their conscience. 

The origins of Trial by Jury, that is the swearing of twelve men to examine the truth of a case  pre-dates the Battle of Hastings, 1066.

The original Jury procedure might be called an inquest, that is the summoning of twelve freemen to provide information to the best of their knowledge on suspected criminals in their district commonly known as the hundred. This process later came to be known as a Grand Jury, the jury which formulates accusations. The Jury described here in Clause 6 is a Petty Jury, or trial jury, that is the jury which decides guilt in a specific case.

Perhaps introduced by King Henry as another anti-corruption measure. The truth of a case in the ecclesiastical court was not to be bought from the archdeacon. The bribing of twelve persons in a jury would be less likely. 

 
References
 
History of trial by jury in England - Wikipedia

William Forsyth; Appleton Morgan (1852). History of trial by jury. J. W. Parker and son

Þorleifur Guðmundsson Repp (1832). A Historical Treatise on Trial by Jury in Scandinavia and Iceland. Thomas Clark.

Jury - Wikipedia

The Jury of Presentment before 1215
Roger D. Groot
The American Journal of Legal History
Vol. 26, No. 1 (Jan., 1982) , pp. 1-24
Published by: Temple University
Stable URL: http://www.jstor.org/stable/844604

Compurgation or the Wager of Law

Compurgation was when a jury of character witnesses [compurgators] was brought into the court by a defendant, each to swear on oath the innocence of the defendant. In Medieval times Compurgation provided a complete defence at law. The essence of the procedure lay in oath making. The compurgators did not have to be actual witnesses of the crime or felony, or have any substantive knowledge about the topic of the case but simply swear that they believed that the defendant was telling the truth. The theory behind the process was that oath taking was serious religious matter in which the eternal damnation of one's soul was at stake.

Trial and defence by Compurgation in accusations brought by the grand jury in the King's court was done away with by the Assize of Clarendon in 1166.

Compurgation - Wikipedia

Francis Palgrave (1832). The rise and progress of the English Commonwealth: Anglo-Saxon period. Trila byCompurgation or the Wager of Law: John Murray. pp. 214–.

Þorleifur Guðmundsson Repp (1832). A Historical Treatise on Trial by Jury, Wager of Law, and Other Co-ordinate Forensic Institutions, Formerly in Use in Scandinavia and Iceland. Thomas Clark.

1911 Encyclopædia Britannica  Compurgation - Wikisource

1911 Encyclopædia Britannica Jury - Wikisource

Superstition and force. Essays on the wager of law - the wager of battle - the ordeal - torture - Lea, Henry Charles

Thomas Edlyne Tomlins (1820). Law-dictionary Explaining the Rise, Progress and Present State of the British Law Etc. 3. Ed. with Additions. - London, Payne 1820. Wager of Law: Payne. pp. 2–.

https://en.wikipedia.org/wiki/Assize_of_Clarendon

The Jurist; Or, Quarterly Journal of Jurisprudence and Legislation. Art. VIII Wager of Law Baldwin, Cradock, and Joy. 1827. pp. 107–. 

jurare dudecima manu

G. A. Louis Henschel; Pierre Carpentier; Johann Christoph Adelung (1844). Glossarium mediae et infimae latinitatis: A-Z. Firmin Didot fratres. pp. 930–.

Benjamin Thorpe. Ancient Laws and Institutes of England: Comprising Laws Enacted Under the Anglo-Saxon Kings from Aethelbirht to Cnut. Cambridge University Press. pp. 637–8. ISBN 978-1-108-04515-5.

Timothy Cunningham (1783). A New and Complete Law-dictionary. Oath - Juramentum: The Lawbook Exchange, Ltd. pp. 369.. ISBN 978-1-58477-274-3.

George Crabb (1831). A history of English law. C. Goodrich. pp. 30–.

Crime, Compurgation and the Courts of the Medieval Church
R. H. Helmholz
Law and History Review
Vol. 1, No. 1 (Spring, 1983), pp. 1-26 

DOI: 10.2307/744000
Stable URL: http://www.jstor.org/stable/744000

http://www.vlib.us/medieval/lectures/law.html