About 91% of female murder victims are killed by someone known to the victim so it is reasonable for the police to start with her close associates.

I don't know anything about this specific case, but in general - we need to adjust this kind of statement for selection bias, and I would like to know how this is done.

When killers aren't known to the victims, the police are less likely to find them both because they don't look for them (as you said) and because there are too many people the victim didn't know for the police to examine more than a small fraction.

Therefore I expect the just conviction rate in these crimes to be lower, and the false conviction rate to be higher (the police are always likely to accuse and help convict someone the victim knew, but in these cases we know such an accused is innocent).

However, your statistic (many murder victims knew their attacker) probably actually counts convictions. How should we revise this due to A) false convictions and B) a different-than-general rate of crimes solved (where conviction was achieved, or the primary suspect died or fled)? If the statistic already takes such considerations into account, how it this done?