there was a lawyer (American) on the show too: he reckoned the prosecution wouldn't stand a chance. You do need evidence.
The best new evidence the show offered was from David Starkey: he'd discovered that when Tyrrell (the supposed killer) was tried, King Henry and his wife (the princes' sister) went along to watch. From this he deduced that something important, like a confession to the murders, must have happened. And, er, that's it.
That really isn't evidence.