I thought all was safe and I got up and called the police.
What made you call the police?
I saw a black man walking around.
If you have witnessed a crime or you feel that you or someone else is in danger, you absolutely should contact the police. Calling the police on someone just because they're black is not right, though.
I am sure that the black person is a criminal. Why else would he be here?
It is very rude to call the police just because you see a black man walking around. He could live in the neighborhood, or he could be visiting someone.