Despite its poor record on freedom of speech and human rights in the past few years, Rwanda's legal system is efficient and relatively uncorrupted. Your main contact with the police will be if you're driving, as dozens of patrols monitor speed limits and you can expect to be pulled over if you travel even slightly over the posted speed. Foreigners are routinely let off fines, however, though being asked for a bribe is certainly not rare. Politely refuse and try to stick to the speed limit. There is a presumption of innocence in Rwanda and a legal right to a lawyer if you are arrested.