Horowitz’ job was not to re-investigate the case, and he said so from the outset. His job was to investigated the conduct of the FBI and DOJ employees. That’s what IGs do. They are not a court of appeals.
What?
Strzok's "conduct" was to ignore evidence that Hillarys emails were sent to a foreign entity. Apparently Horowitz didn't investigate Strzok's "conduct" on that matter. In fact he ignored four phones calls about it.