What would be the scariest movie if every movie was based on a true story?

[NewLion]

Jaws

Perfect Sense. An epidemic causes everyone to lose their senses. It’s terrifying because society breaks down. Imagine not being able to see or communicate with your own children. If you lost hold of them you’d never find them again.

More a genre than a single film but literally every body horror movie even the more silly Z grade ones.