There are numerous synonyms that can be used in place of the phrase "horrifying atrocities." Some options include heinous crimes, appalling acts, gruesome atrocities, shocking offenses, abominable deeds, unspeakable horrors, and monstrous atrocities. These phrases all convey a sense of extreme disgust and horror at the actions being described. They are often used in reference to war crimes, acts of terrorism, or other violent and senseless acts that are committed against innocent people. The use of synonyms for "horrifying atrocities" can help to add emphasis and emotion to a piece of writing, making it more impactful and memorable.