Unsurprisingly, your description is inaccurate. The 3 scientists were instructed by the prosecutor to take random samples and analyze them. The three did that. They did not make the decision of what needed or did not need to be tested except for choosing which "random" samples they should analyze. But that's what "random" means. From Vecchiotti's testimony during the first appeal trial when asked about the Olgiata case:
"
Vecchiotti : Yes, if it’s relevant, the Presidente will decide : I’ve decided to answer, and I presume that it will be. So, the Olgiata case that was brought forth as an example, is a mistaken example and I’ll explain why. It’s not true that nothing was found, you have to start from a premise in my opinion, of knowing what the problem that was set. The problem that was set was this : take random samples….
Hellmann : But, sorry Dottoressa…
Vecchiotti : Sorry, excuse me, it’s not true that I found low DNA, it’s not like that, anyway there were three consultants from the Pubblico Ministero, and we had, the task was given to us by the Procuratore of making limited and random samples, and we have this formulated and written down in the thing ; another exhibit was to be left in suspense and not examined unless he gave his explicit authorization, so in agreement with the parties, we also have the films, we filmed and swabbed the traces, certain traces, as they had said, certain limited traces. It was our misfortune that we didn’t take the trace that contained the DNA of the person who later confessed to having been the assassin, but it was chance, it wasn’t that I had extracted a little DNA, I want this to be clear, it wasn’t that there was a profile or someone else obtained a profile, it wasn’t like that. But that trace…
Comodi : No, you didn’t even find the trace."
So, unlike what Vixen claims, there was no charge of "swapping DNA samples" or , as Machiavelli also claimed, of Vecchiotti "lying". Why am I not surprised?