Depends on locale. In Germany something like 90% of murder cases are solved/cleared.
In the U.S., I suspect a majority of the murders technically unsolved by police are cases where the identity of the perpetrators is somewhat of an open secret within communities that don't trust law enforcement (and LE similarly has little interest in working with them either.)
>In Germany something like 90% of murder cases are solved
You must watch out when reading the German crime statistics. "Solved" which is marked as "aufgeklärt" in those statistics just means that a suspect has been named. Not that someone actually did it/has been sentenced for the crime.
Surely it's pretty common everywhere to have at some point a suspect ('solved!') who is then released, because you lack evidence, realise it's not them, whatever. A suspect isn't necessarily convicted even if you do ultimately convict someone.
Turns out it was someone else, and you convict that other person. You thought you had them, were wrong, but did then ultimately solve the case.
It happens loads too, frequently in high profile stuff on the news they'll have a suspect who's somehow close to it, arrest them, but then they're released once satisfied with their allibi or whatever.
In the U.S., I suspect a majority of the murders technically unsolved by police are cases where the identity of the perpetrators is somewhat of an open secret within communities that don't trust law enforcement (and LE similarly has little interest in working with them either.)