Why the feeling of anger, sadness, and frustration?

In our small town, a 15 year old girl was murdered by her mother's boyfriend who has a rap sheet a mile long. He was also heavy into drugs. This young girl's body was found in an embankment off of a mountain road. I didn't know the girl personally and my daughter was just an acquaintance but I... show more In our small town, a 15 year old girl was murdered by her mother's boyfriend who has a rap sheet a mile long. He was also heavy into drugs. This young girl's body was found in an embankment off of a mountain road. I didn't know the girl personally and my daughter was just an acquaintance but I can't help thinking about how she endured a horrific death at such a young age. I am so angry with this man and I feel frustrated about the situation. I also feel a great deal of sadness when I think about how she had her whole life ahead of her. Why do people like me, who don't even know the victim, feel this way about situations like this?
Update: I would never do this but there are people who are stalking the mother of this young girl on social media and ridiculing her, threatening her, and using expletives that are pretty disgusting. I feel the same anger toward the mother but I don't advertise my anger on social media or outside of my own house.
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