If the fatal bullet was fired by a bodyguard or policeman reacting to Sirhan then Sirhan is still culpable for RFK's death.
And the audio "evidence" just isn't enough for me, some experts say there's 13 shots on the tape but some say only 8. Who to believe? So then we move onto eyewitnesses ... er, better not. Physical evidence? AFAIK it supports Sirhan as the shooter unless someone can put me some knowledge?
I'll concede the first point here.
The second point brings up the crux of the case.
The strongest piece of evidence that Sirhan can hang his hat on is the fatal shot as described in the autopsy report, but in order to prove it they would have to have all the eyewitness testimony to conclude that Sirhan never got behind or beside Kennedy to get close enough to shoot from point blank range. It's an iffy proposition. Noguchi did good work for years and there really should be no doubt on how he determined the cause of death.
In regards to the audio tape, it matters where that recorder was in the timeline of events. We saw the HSCA get fooled on the stuck mike at the Trade-Mart in Dallas. In this case we have a higher quality of recording device, a cassette rather than a dictophone case, but unless there is film evidence of the reporter being exactly where some have claimed him to be, then those impulses or sounds may not be shots. It could very well be 13 shots, or it could be wrong.
There is no film record of the actual shooting. We have Gordon West's audio recording of Sirhan's apprehension, but IIRC no shots of him firing are on that tape.
The place was a madhouse. An overcrowded hallway on a hot night that saw shots. There was no real security. There was very little secured. LAPD weren't even in the building.
Press photographers were there and took shots of the aftermath and investigation. There has always been some question as whether 8 shots were fired and how many bullets could be accounted for in walls, doorframes, people, or elsewhere.
Sirhan got caught with a fired gun in his hand. He's not innocent here.
The problem is he has some plasuible outs. I think the odds are 70/30 that it's just him. I'd go with a 20% chance that the polka-dot girl seen coming out and another male are in on it. Eyewitnesses testified that she bragged about shooting RFK including campaign volunteers and others, yet nothing solid has come out since then.
The security guard shooting after seeing Sirhan shooting, I'll give that a 10% chance. It would explain a head shot and the guard was no Kennedy fan, but the thought of taking a potshot at RFK out of the blue because someone else is shooting seems a bit far-etched. Yet, truth is stranger than fiction.
Having such a public crime scene with such a public figure would give even the best police department fits on doing an absolutely correct and through investigation. We know that the LAPD might not fit that description. I'm sure based on what law enforcement learned based on Dallas that they were in over their heads. They also knew they had Sirhan wrapped right up and the chances of not getting a conviction were nearly none.
They got a lot of it right, the question is did they get everything right. As time goes by, it looks better and better for them.