Someone living in your home is known to you

> “Overall, 76% of female murders and 56% of male murders were perpetrated by someone known to the victim.”

> https://bjs.ojp.gov/female-murder-victims-and-victim-offende...

Lets say M is "being murdered" and A is "stranger in the house", "not A" is "person known to the victim in the house".

The numbers you're quoting say that P(not A | M) is large, implying that P(A | M) is small.

However, to make a decision on whether to let someone in, I care about P(M | A).

You need to exercise that critical thinking more. You just heard someone say "the murders are known to the victim" and you instantly dropped your common sense.