Thinking someone is 100% guilty is not the same as knowing or proving beyond any doubt that someone is 100% guilty.The trouble is though, what happens when we have someone we think is 100% guilty and it later turns out they're not?
I'll try and find an example or two later.
I would say the minimum criteria for establishing absolute guilt would be:
Evidence of premeditation
Multiple witnesses (i.e. crowded public place)
Multiple CCTV/mobile phone recordings
Perpetrator arrested at the scene
DNA/forensic evidence
Admission of guilt
If you can find a miscarriage of justice where the innocent party was convicted with all the above being proven in court, then I'll eat my proverbial hat.