A 75 page paper usually takes longer than 48 hours for normal students to write. If the version history for the paper is submitted, but all the commits are within a very short time frame, then either the student stayed up all night to write it, or they paid someone else to stay up all night to write it. And if you ask them about what the wrote on on something they took all night to write, they should know it fairly well. But if they paid someone else to do it, they wouldn't know anything that's on the paper.