Looking five times... it is a bit unlikely that they wouldn´t have spotted it, even though they weren´t specifically looking for it. What WERE they looking for then?
One was pretty snotty and rejected the claim he did a poor job by not finding it. He claimed they were not told to look for it and he only took items he was told to. He made it seem like he was following strict orders of his superiors almost as if bitter at them or something. "I did as I was told and nothing more" as if his bosses were Nazis or he was just a lazy slacker. Others suggested they were just looking around to see if there was anything that popped out as significant. They were not as nasty while being interviewed.
We don't know for sure if the suppressor was there or not. For all we know Jeremy put the box that had the ammo carrier and suppressor in subsequently. But more likely police just didn't think it was of any significance because they were told a story of the gun being left out without the suppressor attached so figured it had no relevance. They were aware of other firearms yet left them not just the accessories and bullets. They decided too quickly not to pursue it as a homicide and take everything. They didn't even call the firearms expert to the scene.
They had way to many people on the scene getting in eachother's way and not knowing what the others did. To not call the firearms expert though just because they felt it was murder suicide seems pretty stupid. So they have everyone galavanting around except who they should have.
They took photos, then moved things then others moved them back for more photos, then they moved them again and others moved them yet again for more photos. The left hand did not know what the right hand was doing. None of this kind of crap would have happened in 2014 so we would have a much clearer picture of certain things.