I don't think statistics are relevant at all. Suppose the stranger is wielding a kopesh, an ancient Egyptian sword. What we want to know is not "how many murderers use kopeshes?" (none of them), but "is this guy a murderer?", and that seems in line with what you're saying about statistics. However, the question "how many wielders of kopeshes are murderers?" is also irrelevant, and the answer is still none of them. Similarly, "how many strangers in your house have been murderers?" is irrelevant, even if the answer is "all of them so far". Perhaps you only ever let one stranger into your house, and once inside she killed somebody with an arquebus, and you said "never again" - but that would be paranoia. Perhaps you look at country-wide statistics for the average stranger (these aren't kept), but you are not personally country-wide, and the specific stranger is not an average. What's more, if you befriend the stranger, what statistic do you want to use then? The thing to do is reason, not count. I think the 76%, 56% statistic (although irrelevant to a decision) is attempting to say a lot of murderers are motivated by interpersonal relationships, you know, and get you to think about what a given person might be up to, or might want, and the extent to which you can even tell, and the value of risking the unknown.