Re: Verdict decided then
> imagine someone standing over a dead body, knife in hand, victim's blood all over them.
> They would be charged with the murder
Yep, but it's up to the prosecution to prove they did it, not the defence to prove they didn't. The argument would be perhaps "I found the body", it's up to the prosecution to find forensics, witnesses etc. to show they killed them.
> How about if there was an illicit video recording of the murder?
You mean the killer recorded himself doing it? It would depend how the police got the video. If it was the result of an unwarranted search (e.g, they dug through your phone during a traffic stop) the video would be excluded - that's the "fruit of the poison tree" thing.
It's not a "technicality" (IMO), it's the rule that says police can't just wade in because they feel like it, they have to have evidence you did something wrong.