No, the other way. More like 50-60% are solved - as in, we know who did it - but in some of those we can't arrest the guy 'cause we can't find him or we don't have enough evidence.
OTOH, not all of those arrested are going to end with convictions. And a few of those convictions are just wrong -
Reason Magazine - Hit & Run > Eddie Lee Howard: Mississippi's Next Exoneration?