There's a couple things that you need to complete before you can confront McAdams. I can't tell from your post which one is it but there are two things to complete here.
One of them is in the Art Room:
You need to use your postcog power on the orrery to learn something that you need to know about to be 100% sure for
You also need to show McAdams an inventory item:
Show him John's lighter to prove that he's in the Towers
You also need to check your dossier:
One of Terence's messages on the dossier mentions that the case was super misfiled. Erica needs to read that dossier entry in order to confront McAdams
You should be able to confront McAdams after having done these three things. Have you already done this? You should get a new dialogue option for McAdams called "Confront McAdams" or something similar.
There's a couple things that you need to complete before you can confront McAdams. I can't tell from your post which one is it but there are two things to complete here.
One of them is in the Art Room:
You need to use your postcog power on the orrery to learn something that you need to know about to be 100% sure for
You also need to show McAdams an inventory item:
Show him John's lighter to prove that he's in the Towers
You also need to check your dossier:
One of Terence's messages on the dossier mentions that the case was super misfiled. Erica needs to read that dossier entry in order to confront McAdams
You should be able to confront McAdams after having done these three things. Have you already done this? You should get a new dialogue option for McAdams called "Confront McAdams" or something similar.
The lighter! Thank you very much, now I can carry on :)