Well, if all you've got is that the person has a briefcase with one person's information in it, then presumably if that's all there was, perhaps you shouldn't be getting a conviction for possession of identity information in circumstances giving rise to the intent that you might use it. And in fact, that might be true. It might be true that they've simply found a briefcase.
But if they have a briefcase with identity information relating to 50 people in it, or if you investigate and find that the briefcase was stolen, for example, and that person fits the description of somebody who might have stolen it, you may actually have physical theft of the briefcase.
What you're stating is the very reason why we require the showing of some evidence of at least circumstances that suggest they have the intent to use it for a further offence. You could well have a case where somebody loses a briefcase, somebody finds the briefcase, and they've acquired it quite innocently.
Now, have they made any efforts to return it, and so on? All of these might be relevant circumstances, but if all you had was simply the person and the briefcase belonging to somebody else, there might well be that sort of innocent explanation.