I think that people who are suppose to become cops should already have a idea that they are there to protect and serve their community. If any person were to become a cop and not want to protect and serve the people then they should be removed.I think cops raping women who they arrest is rare. Most people become cops to help people not hurt them.
I don't think it depends on the country, but rather the person. Most people are good at heart, but if they have issues like something against women, they may rape. Police who do this are sick individuals and these incidents do occur. However, they are not limited to police alone.
You can never be sure whether it happens often or not. Despite it not being in the news, that doesn't mean that it doesn't occur. Some stories are either not big and turn a blind eye or people just are better at not getting caught.I haven't heard of anything like this happening in the U.S. lately. However years ago there was an incident I read about. It occurred in New York City. There was a police officer convicted of raping immigrant cab drivers. He would pull them over for traffic violations, handcuff them and sodomize them in some isolated area. Most were so ashamed that they kept quiet.
In another incident, also in New York City back in the 80's there was a police officer who was released from the force for exploiting young prostitutes. Forcing them to have sex under threat of being arrested. There are always going to be a few bad apples.
In most of the countries in Africa,police are well known when it comes to rape while arresting ladies.
I always pity our ladies who suffer a lot that some get infected with very dangerous diseases like aids among others.