It is to be observed however, that, in a case such as this, when there is found in the possession of prisoners some implements which might have been used to commit the crimes charged and other implements which could not be put to that unlawful use, it is not always an easy matter to apply the principle which acknowledges the admissibility of evidence of the possession of tools of a burglar to identify the accused with the crimes charged. The principle of completeness might sometimes dictate that evidence should be admitted going beyond proving the possession of tools which might have been used to commit the crime in question. While recognizing this, however, we are satisfied that in this case, where a collection of tools was found, the detailed evidence of the use to which some of the tools, which, it is clear, were not used in the crime might be used by a thief to commit other crimes, was no more than evidence of a particular criminal propensity, i.e., the propensity to steal from safes, and of the means to indulge that propensity. This conclusion is reinforced by the use made of the evidence by the learned trial judge, who referred to the proof of the possession of the "kit" as a whole as "evidence of tell-tale articles" and as "evidence of suspicious articles" or "suspicious instruments". In this way, what was admissible as evidence of identity, if it were admissible at all, was given a wider and an unjustifiable significance. Of course, evidence which is admissible because it is relevant does not become inadmissible because it also tends to prove the criminal propensity of a prisoner, although a judge should, in a proper case, in the exercise of his discretion, reject such evidence if its prejudicial effect is out of all proportion to its probative value. Furthermore, when evidence is admitted which is relevant but which also shows criminal propensity, a judge should explain the limited use that can be made of that evidence. In this case, however, we have come to the conclusion that the admission in evidence of the tools which could not have been used to commit the crimes charged, and the admission of evidence of the suitability of those instruments for the commission of other crimes, did nothing to connect the prisoners with the crimes with which they were charged beyond telling the tale of their criminal propensity.