Plagiarism & Copying - Help Identifying

Word - Ownership Properties

If the student is on a computer that someone else logged into, then anything created and/or modified will automatically have the other computer owner’s information attached. 

It is possible to change the author:

But, if you go to File and check the document properties, they still show the computer “owner” as the last modifier regardless of whether or not, the author has been changed:

There isn't a definitive way to tell who actually wrote a paper based on the computer assigned properties.