From my earlier post, I think I figured it out
He's trying to prove that George lied about the list of family inventory of guns because that list contained the weapons they took to the murder, one of which was proven used in the murder, and were later all dumped in the pond. George was aware of the guns on that list that were used in the murders and lied about the list. That means he was part of the conspiracy.
Prosecution has to go through all of this thoroughly so the defense doesn't cast doubt on the evidence by saying they have no proof that this that or the other gun was used in the murders or was on the list that George lied about because he was trying to cover up their involvement in the murders.
Remember also, the use of the silencers both ties them to the crimes, carries separate charges because they are illegal and are also part of the evidence used in the crimes that George helped build and test.
So far, this goes towards proving charges for
Specification 2 of each of the 8 Aggravated Murder Charges Count 1 through 8
Count 9 - Conspiracy - George lied about the list of guns, which included those used in the murders
Not sure if Obstruction of Justice would apply