It could be evidence from blood tests. It's unlikely an accused would have that type of evidence. It would likely be in the sense of testimony that the accused provides about what they consumed. There could be other witnesses who might testify as to the state that the person was in at the time. The reason the accused must prove the defence on a balance of probabilities and with expert evidence is that the accused will be in possession of that type of evidence. That's why the common-law rule sets out that the accused must first prove that they were in that state before the court will accept the defence.
