system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] How did anyone know that Voldemort attacked the Potters?

So here is the timeline that I'm aware of:

-Voldemort shows up at the Potter's house.

-Voldemort kills James.

-Voldemort kills Lily.

-Voldemort tries to kill Harry and fails.

-Hagrid shows up to get Harry.

-Hagrid arrives at the Dursley's. Based on the conversation that Dumbledore, McGonagall, and Hagrid have, it sounds like Dumbledore has not been to the Potter's home (or else why would he not have brought Harry himself?). Also, Hagrid said that the muggles were just starting to swarm around the house, indicating that it he was there very shortly afterand that he was the first on the scene. (Again, if someone else was there earlier, why didn't they take Harry somewhere else?)

How did Hagrid/Dumbledore find out so quickly?
gpt
There were more magical wards than the Fidelius Charm around the Potter's house. When the killing curses started flying Dumbledore was instantly alerted through a localized Taboo on "Kedavra." 

Unfortunately, Voldemort anticipated this and shielded the area from unwanted apparition for the time he was there.