30 Anciently, no person could be convicted of the small est offence till he was found guilty by a jury of his country men ; and though now, for more than a century past, infe rior judges have tried lesser breaches of the peace de pia no, yet to this day all prosecutions of a higher nature, whether before the supreme or inferior criminal courts, must proceed by jury ; and no trial, even for a blood-wit, if pursued before the justiciary, can he carried on without a jury. In the trial of crimes competent to the court of session, the judges may well be considered in the character both of court and of jury.
31. Crimes cannot, like debts, be referred to the defen der's oath ; for no pet-son is compellable to swear against himself, where his life, limb, liberty, or state is concerned ; nor even in crimes which infer infamy, because one's good name is, in right estimation, as valuable as his life. The law is however forced, in the crime of usury, to depart from some of its common rules, that the crime may he brought to light. Where the usury is founded on a written obligation, in the hands of the defender, the put- s let may, by an exhibition, force hint to produce it in evidence of the crime, contrary to the rule. .A"emo tenetur edere instrumen to contra se ; and where it is not founded upon writing, the clime may be proved by the usurer's own oath, notwith standing the rule, Arcmo tenetur jurare in seam turIzitudi nem, 1600, c. 7 Crimes therefore are, in the general case, proveablc only by the defender's free confession, or by writing, or by witnesses. No extrajudicial confession, un less it is adhered to by the pannel in judgment, can be ad mitted as evidence ; for the whole proof must be deduced in open court, in presence of the assize, or jury, as well as of the pannel. A judicial confession ought to be received with all the qualities that the panuel has thought fit to ad ject to it; so that the prosecutor, who pleads upon one part of it, must admit the whole. Proof by writing is seldom used but in usury, forgery, and perjury. Though, in de foreement, the written execution of the messenger or offi cer is sufficient evidence of the violence in all civil ques tions concerning the validity of the diligence, till it be de clared false ; yet in a criminal trial moved against the dcforcers, the messenger's execution, who is a party inte rested in the prosecution, is not regarded.
32. All objections relevant against a witness in civil cases, arc also relevant in criminal. No witness is admit-, ted who may gain or lose by the event of the trial. Hence;
in the crime of usury, the testimony of him who has given the unlawful profits is rejected, because he becomes a gain er by the conviction of the usurer, 1600, c. 7. In deb:tree ment, the persons employed by the messenger to attest the execution are in some sense parties, violence being com monly used against them as well as against the messenger ; yet, as the proof of the crime would be frequently imprac ticable if their evidence were rejected, the law considers the messenger as the only party against whom the violence is intended, and therefore receives the testimony of the wit nesses, though they should be beaten. Socii criminis, or associates in the same crime, are not admitted against one another, except either in crimes against the state, as trea son ; in occult crimes, where other witnesses cannot be had, as forgery; or in thefts or depredations committed in the Highlands, 21 Geo. II. c. 34. 21. The testimony of the pri vate party injured may be received against the pannel, where the king's advocate is the only prosecutor, if, from the nature of the clime, there must needs be a penury of witnesses, as in rape, robbery, &c.
33. Where a crime is to he proved by several circum stances connected together, every one of which makes a part of the same criminal act, a single witness to each cir cumstance, is sufficient evidence. But it may be doubted, whether this ought to obtain in crimes reiterated by differ ent criminal acts ; for if a single witness should be deemed sufficient in such case for proof of each separate act, it would destroy one of the strongest checks by which the testimony of false witnesses may be controlled. Formerly, the depositions of witnesses in all trials before the criminal court were reduced into writing ; but that practice is abo lished by 21 G.:o. II. c. 19, unless where the libel concludes for death or demembration. Crimes which, by their na ture, hardly admit direct evidence, may be proved by pre sumptive evidence ; and these presumptions ought, from the severity of the conclusions in criminal trials, to be so pregnant as necessarily to carry conviction along with them. But where a crime is to be tried only ad civilem effectum, e. g. where a process of adultery is brought for ,obtaining a divorce, more slender presumptions will be re ceived ; so that the same proof that has been judged suffi cient for procuring a divorce before the commissaries, may be cast, if the crime should be afterwards tried criminally.