You're accepting his assertion it's all hearsay and lies
I'm no lawyer but if I'm not mistaken, the general exception for hearsay being allowed in court is if someone told me something and is now dead, I may testify as to what he/she said. If they're alive and in heath enough to appear in court, the requirement would be they would have to testify.
I'm not certain as far as me testifying to someone making verbal threats against someone else in my presence, but I think they're generally accepted.
What isn't accepted is what you're describing. I may testify as to what you said to me about your intentions and actions. Except in very narrow circumstances, I'm not allowed to testify as to what you told me your best friend said.
That's my general understanding.
But your outcry about justice system being corrupted is accepting his claim he is only convicted on hearsay. Your own link only recounts his claims, how does it support or deny those claims? It doesn't even attempt to, it just reports what he claims to deny his guilt.
So why do you accept that as prove the system has failed?