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:

Word 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:

Word Properties

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