I think what Harry would say is that he was running it like an experiment. He can say he was sure that he would be the next target for the traitors, so he split the other players into two groups - Group A that knew he had a shield, and Group B that didn’t.
if someone else got murdered that night it would suggest that Group A has one or more traitors, because it was only the fact that a traitor knew about Harry’s shield that saved Harry from murder.
Because no one is getting murdered, Harry can say that the traitors must ALL be in Group B - because he can spin the story that the traitors tried to kill him and failed so they obviously didn’t know about his shield.
That rules out Group A - Mollie, Jaz and Zach - having any traitors in it. They all knew he had a shield so wouldn’t have wanted to waste a murder.
He doesn’t need to have trusted the members of Group A when he told them about his shield, because they were all being “tested”.
I think he is going to try to create mutual trust within Group A and get them all focussing their suspicions onto Group B.
if it works that would buy him time for someone in Group B to be banished (Jasmine?), and then probably someone in Group A would be murdered the following night (Jaz or Zach, keeping to the narrative that the traitors are all in Group B).
I hope that’s what he is thinking as I’d like to see it play out! Still lots that can go wrong, and the other traitors may be the threat he is underestimating.