Nedbank
Suspecious substance

Hi can someone please advise me what to do. I work in the same office park of one of the nedbanks On several occasions I've noticed that one of their employees exchange something with others in the same office park. During last week i had a clearer view of what is exchanged and it was marijuana in exchanged for cash. I'm not sure if i should report the matter to their hr or to the authorities. Please advise. Thanks