At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
Who (whom, whomever) refers to people. That and which refer to groups or things.
The party referenced is a group. In this case, "police" are the ones being referenced. i.e. ...police said.
I believe you need to use the word "that."
Thanks for the reply, but the party referenced here is not police. The party referenced is the student. Either way, police are people, too. I received a reply outside of this website that the correct answer is who. The inclusion of "police said" into the sentence does not change the rule that when you're talking about the subject part of a phrase, you should use "who" and when you're talking about the object part of a phrase, you should use "whom."