It needn't be detectable. Having said that it seems like an odd thing to have done, particularly in such a way to be undetectable. You'd then have to go down the road of the crime having been elaborately planned well in advance.Until the report is presented in court it's speculation that has been reported as probable. When it is, I'm sure they will explain why they believe it was human activity. It is possible it could be scripted but I suspect that would be detectable.
If it proves human interaction to the extent that you clearly suspect, then it's powerful stuff. In and of itself its all but enough to completely prove their innocence. It would be funny, in a bewildering and sad kind of a way, if they had had an alibi all along, but had forgotten/hadn't realized it. The Wizard of Oz ending:I'm not sure what other ways would deactivate a screen saver shortly after it came on then without leaving an obvious pattern.
Dorothy: Oh - will you help me? Can you help me?
Glinda: You don't need to be helped any longer. You've always had the power to go back to Kansas.