@NonPlayerCharacter
He got the shield and showed it to a few people so they knew he had it (Mollie saw him get it so she already knew). The next morning, after recruiting Ross, he explained the fact they were all there at breakfast by him having the shield, saying the Traitors must have tried to murder him and failed. Then later he said the Traitors couldn't be anyone who knew about the shield, because if those people were Traitors, they wouldn't waste the murder. It pointed the finger at those who hadn't known.
I'm pretty sure Harry didn't do any of that.
It was Zack.
Harry told Zack, Jas etc the night before, but in the morning it was Zack that got excited and started telling everyone the theory. Harry then sat back and let Zack run with it. That was Harry's genius. He fed Zack ideas and off he went 😂