I wouldn't tell on him even if it wasn't my friend. Cheaters will eventually get caught. But to be honest, If you were focused on your own practicum, you wouldn't know what the next person is looking at. Just let the professors do their job, you do yours.
That's like calling the cops on someone who downloads pirated music.
However, I might talk to him afterwards about it, but I wouldn't go to the professor. Somethings are not worth losing friends over. On the other hand, if my friend shot, killed or sexually assaulted someone, I'd report them to the police real quick.
If you think about it, police see people break laws all the time (j-walking etc.), but they pick and choose what to enforce because they can't stop everyone. Devote your time to more serious issues.