According to Merriams, an "atrocity" is
1 : extremely wicked, brutal, or cruel : barbaric
2 : appalling, horrifying
3 a : utterly revolting : abominable <atrocious working conditions> b : of very poor quality <atrocious handwriting>
Compare that to mere brutality:
2 : befitting a brute: as a : grossly ruthless or unfeeling brutal slander> b : cruel, cold-blooded brutal attack> c : harsh, severe<brutal weather> d : unpleasantly accurate and incisive
brutal truth>e : very bad or unpleasant brutal mistake>
It seems to me that some acts go far beyond merely brutal and are "atrocious." Such as shooting a woman who is holding a baby in her arms, and flipping an 84 year-old woman so that she falls on her head and begins to bleed. These acts are not merely brutal, which is a description of the act itself, but these acts go beyond brutal to also being atrocious, because WE find them to be "appalling, horrifying", "wicked . . . barbaric", "utterly revolting" and "abominable."
Consider the case of Esteban Carpio. Turning his face to hamburger by repeatedly punching him in the face was brutal, but then bringing him to court like that for him family, with his face covered by a white Batman mask whose only purpose was the evidence which nonetheless made people in the court sick was an atrocity that no one will forget with respect to the Providence Police Department.
If the police behavior you are describing is merely brutal, in your intellectual opinion, but does not make you FEEL revolted when you hear about it, then stick with the word "brutal" and call it "police brutality."
However, if you are appalled and horrified by a police act and you find it utterly revolting, then step up the rhetoric and call the act what it is: a police atrocity.
I guarantee you that when we start using the word "atrocity," the media will notice, because an "atrocity" is on a whole different order of barbarism and revulsion than mere brutality.
Much of what police do to Black people goes beyond brutal and can only be described as an atrocious. Let's not oversuse the word atrocity, but let's use it when police behavior goes beyond their normal brutality and reaches into the realm of appalling, revolting and horrifying barbarism.
Remember (Francis): atrocity only has one "t".