Mark Duffy is a student at Hudson University and a staffer at its Snack Max. He was a customer of Caroline Pereira in regards to her plagiarism-for-pay scam regarding university papers.
When Caroline was murdered, Mark was questioned at his place of work. He elaborated exactly how she ran her operations, all the way down to her paymepronto.com private pay account. He remembered Brian Townsend lost it when Caroline's scam was about to unravel, but Brian was just trying to bribe her silence, which she laughed at because of how easily she could illicitly come into money. (SVU: "Class")