Yet, he had ammo stashed in his hotel room for a 9mm. Only someone with legit mental illness would buy or being direct possession of ammo for a weapon they have no access to. WH had access to a 9mm. No question in my mind. He just fancies himself smarter than LE (as most seasoned felons do) and believes whatever he (or someone else) did to conceal the actual gun, was enough that LE would never find it.
The gun could be hidden in plain sight like Edgar Allan Poe's "The Purloined Letter". Looking for a 9mm handgun is like looking for a 'white car' - it's probably the most common handgun caliber in the US. Anyone of WH's friends or relatives could be in possession of one. VA does not require registration of handguns. Without more details, LE has no idea of what they are looking for. If there are photos of WH showing AJ how to shoot - like he said he did do - maybe LE can narrow it down.