“Certum est, et commune apud omnes quod, ex justa causa, licitum sit uti aequivocatione, et cum juvamento affirmare: Et justa causa esse potest quicunque fines honestus ad servanda bona spiritui vel corporali utilia” (Sal: Nos. 109 and vol. sauch).
“A culprit, or a witness, questioned by a judge, but in an illegal manner, may swear that he knows nothing of the crime about which he is questioned, though he knows it well, mentally meaning that he knows nothing in such a manner as to answer.”
When the crime is very secret and unknown to all, Liguori says the culprit or the witness must deny it under oath. Here are his own words:
“Idem si testis ex alio capite, non teneatur deponere: Nempe si ipsi conotet crimen caruisse culpa, vel si sciat crimen, sed sub secreto, cum nulla proccesserit infamia.”
“He may swear that he knows nothing, when he knows that the person who committed the crime committed it _without malice_ (as affir. Salm. to c. 2, No. 259, and Elb. No. 145); or again, if he knows the crime, but secretly, and that there has been no scandal” (as we are assured by Card. No. 51.)
“When a crime is well concealed, the witness, and even the criminal, may and even must swear that the crime has not been committed!
“The guilty party may yet do likewise, when a half proof cannot be brought against him.”
“Reus vel testis non tenetur judicio, respondere si crimen fuerit omnis occultum tunc enim potest imo teneteur testis dicere reum non commisse. Et idem potest reus, si non adsit semiplena probatio” (Salm. D. 2, No. 146 Bus.).
Liguori asks himself (Quest. 2): If an accused, legally interrogated by a judge, may deny his crime under oath, when the confession of the crime might cause his condemnation, and be disadvantageous to him? and he answers:
“It is altogether probable that when the accused fears a sentence of death, or of being sent to prison, or exiled, he may deny his crime under oath, understanding that he has not committed this crime in such a manner as to be obliged to confess it.” Here is the Latin text:
“Quæritur 2. Au reus legitime interrogatus possit negare cimen, etiam cum juramento, si grave damnum, ex confessione ipsi immineat satis probabiliter, (Lugo de Justitia, D. 40, N. 15; Tamb. lib. 3, etc.); et aliis pluribus dicunt posse reum si sibi immineat poena mortis, carceris, rut exilii, negare crimen, etiam juramento, saltem sine peccato gravi, sub intelligendo; se non commississe quotenus teneatur illud fateri mado sit spes vitandi pœnam.”