It’s not exactly common practice to solely use the suspect’s, in this case the cops’, version of events, with little corroboration, when determining the facts of the case and present that to the grand jury. It’s likely, the same cops, who repeatedly lied previously, would also make up events to justify their actions. The AG neglected to mention that 12 people also stated the cops did not announce themselves and corroborated Walker’s version of events, instead. That alone is enough evidence to indict and take to trial, especially since they shot a 3rd party—which does not fall under the Kentucky self defense statute.
So what if the 12 witnesses who didn't hear the cops announce live down the hall, or on another floor? And the witness that did hear them lives right across the hall? It's moot regardless, as they were not required to knock or announce themselves.