I’m struggling to find a reference, but I’ve already seen this used in the reverse during interrogations.

You use something like an EEG and show someone a series of images to establish a baseline of “familiar” and “unfamiliar.” Then you show them photographs of the crime scene that haven’t been made public to test for familiarity.

I question its accuracy but your scenario already seems possible.

Edit: for siblings comments about journalists - “identifying” a source could probably be “accomplished” using the above technique already, no need for AI. Show photos of random people mixed in with the photo of the suspected leak in your gov. department.