+1
I was in a fraternity. Most fraternities on campus have "librarys" in which seniors & Juniors place old exams (assuming the prof lets you keep them), returned homework assignments, Lab reports & papers for the younger members to study from. At my school not only is it allowed, but recommended to study from old test materials.
Depending on the most common major in your fraternity (usually it's business, econ, or biology) the fraternity library could have everything you would ever need as a student or almost nothing useful to you.
Other times fraternities will trade pdfs of study materials. I've seen frats with lots of science majors work with business focused frats to improve their study material librarys. Science guys need the old exams for my school's killer econ courses, and the Business guys need help with the insane chemistry tests.
On a more related note, my chem 102 prof
let everyone keep their old exams. He also kept the exams 90% similar to the previous years. Seriously there is no way he didn't know people had backtests with every question on them. He even told people who failed "if you re-take this course, keep your old exams and study from them." The guy was a huge stickler during lecture, but looking back I realize he was one of the coolest professors I ever had.
On the other hand, I know a genetics professor who kept his exams the exact same. Then, this last year on the final exam (which he lets students keep) he kept the 1st page the same, and the other 14 pages completely different. More than half the class failed the final and he stood up and told them "It's good to use the resources available to you, but always be prepared for a curveball." smirked and then dismissed class. Nobody had the balls to petition their final grade
If the old exams were obtained dishonestly (as you say), then your classmates are cheating. I would stay out of the entire situation, but I would report them if I was somehow involved (the exam was sent to me via a group text and now I could be pulled down with the rest of them).
Either way, unless you are graded on a curve this doesn't effect you much. Your goal as a pre-med should be to get a perfect score anyway, who gives a crap how the rest of your class does. Study hard, get a 100 and tell the rest of them to get lost, because you did it the honest way.