Arrows to move back and forth to find the "discrepancy" could also be an option. Maybe display the full conversation chain once, then let the player move forward and back to present the evidence, which triggers the evidence check?
The issue I had with the fast forward is that I kept overshooting cause I'm kinda dumb and slow to turn it off.
Either way, I'm sure I'll be pleased with your solution! Your consideration (and reply!) is greatly appreciated.