"Atrocity" is the act itself, not the person who commits it. There is a multitude of words that describe evil people, but most aren't strong enough for what you want to say. I suggest words that refer specifically to evil: evildoer (or evil-doer), malefactor, fiend. I would avoid words like "brute" that refer to animals because, after all, animals are not evil.

I think you mean DID something cruel rather than MADE. (I know it's the same verb in many languages, but not English). If they MADE something cruel, that would be as if they invented chemical weapons or something. You could call someone an Atrocity, sort of in a slang way. It would imply that their very existence is a horrible thing.

In speech, we often use ‘atrocious’ to mean ‘bad’ but not related in any way to ‘atrocity’. For example, His spelling is atrocious. Her accent is atrocious. Because of this, ‘atrocious’ might sound weak for actual atrocities. You would say ‘The soldiers committed atrocities during the war.’ We also ‘do something cruel’, not ‘make’.

The correct word is atrocity. (Plural: atrocities) It means " an extremely wicked or cruel act, typically one involving physical violence or injury" and is normally used for war crimes. Since it's a noun, you can't use it like this. However, you can say "someone has committed atrocities", meaning a cruel act.

You say "can I call people...". There are many adjectives, but if you are looking for a noun then it is more difficult. "Monster" is often used in the media and everyday speech to describe a person who has done something cruel. However, that word is also really closely linked to mythical creatures, and therefore some people say that it's not really an accurate explanation of what a real person has done. In a similar way that we might call a person who does good things a 'hero', but it's also possible to criticize that choice of word because it's not very specific. More specific choices are words like criminal, murderer, villain, brute, villain, sinner, etc... but it really depends on exactly what the person has done. People also use words like psychopath and sociopath, often without knowing what they actually mean.