Adrian Monk: Fujikawa. It's from the caddy's cell phone. Walsh must've switched batteries. That morning, Walsh put a new battery in the caddy's phone. One that wasn't charged yet. He had to be sure the caddy couldn't call for help.
Sharona: Is that it? Is that proof?
Adrian Monk: No, he could explain this. But maybe...
Natalie: What? What?
Adrian Monk: The caddy's cell phone. If the new battery is still inside it, it would have Walsh's fingerprints all over it. He'd have a hard time explaining that.
Natalie: My God, we have to find that caddy.