Yes, and even if not, testimony alone is evidence, even if it doesn't lead to other evidence.
It may or may not be evidence that a trier of fact views as credible or sufficient on its own to meet the applicable standard of proof, but it is evidence.
Because founding and running an anti-virus company for a while gets you invited to all the big shots' murder rampages...?
Was he ever even a largish campaign contributor, or anything that might have got him hobnobbing with (people that later turned into) The Powers That Be? I've never heard anything such about him; have you?
Yes, I can. He was no Epstein; he didn't extortionably frolick around on his yacht with underage girls and politicians, billionaires, and celebrities of science, media, and entertainment. The only commonality McAfee's sad "frolicking" had with Epstein's was that it was on his yacht. But it was with his ex-hooker wife, crew and servants, and Idunno what more-or-less temporary "friends" and other hangers-around he may have picked up. Sure, some of the latter may have been second- or third-rate celebrities in their Latin American or Southern European home countries. Do you think that's the kind of people who have the clout to have someone "whacked" (or even the reputation to need "I snorted bathsalts with John McAfee on his yacht" suppressed)?
I mean, sure, I'm perfectly prepared to believe that he might have had some "whackable" knowledge, after all... As soon as anyone presents even a shred of evidence for that. But as far as we know, he didn't have any inside knowledge that needed to be "silenced". That's the null hypothesis; it's claims to the contrary that need evidence in their favour so as not to be dismissed out of hand.