

My guess would be that it was a note on some form of digital media. Say you make a document on your computer that you later delete. The data doesn’t actually get deleted, your computer just removes the location from it’s giant table of contents and marks the space “available to write”. Typically that information can still be retrieved using software tools until it is actually overwritten, and even then there are exceptions. So yes, it is entirely plausible for them to have forensic evidence of a note that someone attempted to destroy.
Maybe I should have left that out, that’s just me analyzing it too much. But lets say you shred a document. You would probably say that you’ve destroyed that document. If someone then took the pieces from the trash and painstakingly put them back together into a readable document, did you still destroy it? Or did you attempt to destroy it?