He wasn't convicted but most people know the truth.
Did Hitler die in the bunker? According to the Soviets, they found his remains.
Did Hitler sign off on the Holocaust? There is no paperwork that proves Hitler know about what his subordinates did.
Is Elvis really dead and did he die in 1977? Rumors abound.
Is there absolute proof that a certain chief executive did terrible things in the shower to a close relative? No, but a lot of anecdotal proof and the urgent reaction of law enforcement to quash such rumors.
Sometimes, you just don't have "absolute proof" about a lot of things but you know them to be true.