Possible Clues:

• Tried to follow a source of trouble and gave evidence
• Certified
• Affirmed by oath
• Witnessed a trial with a boy around
• Bore witness to a tenor put through his paces
• Present for trial, editor provided evidence
• Affirmed
• You'd have sworn that the non-drinker had got the steed broken
• Declared to be true or genuine
• Certified, vouched