Re: vocabulary in this meaning, vouch and attest are only ever used as verbs ("I can vouch for his presence last night" "I can attest to his honesty"). The noun form might be technically ok, but no one ever uses them.
'An evidence' is never correct in this scenario. Normally you refer to an item OF evidence. In this case, you could say "He has to appear as evidence", which would imply they were more interested in something about his body like a wound or scar than what he actually had to say. 'An evidence' can be correctly used like this: "Falling is an evidence of gravity" |