The substance called “Luminol” that they use on those CSI shows actually exists, and you can buy it online. It reacts with blood and other DNA-bearing substances to glow under UV light.
Although Luminol reacts to substances other than blood, apparently it’s very bright when used on a blood stain, and can detect traces many years old and invisible to the naked eye.
Google “Luminol Blood” for way more info than you’d ever need.
I thought just a black light by itself will cause most body fluids to glow? And that Luminol just makes the blood glow more, so it’s super easy to find?
Of course, I am fully ready to admit being mistaken.