In 1912 forensics was still in its infancy when a pretty girl was found dead in her parent's parlour. Her boyfriend was the immediate suspect, but he had an alibi that couldn't be broken. Here's how make-up, and the people who analyse it, broke it.
Marie Latelle's murder, in her own parents' house, shocked the town of Lyons, France. She was a very popular girl. It was her popularity that first pointed police in the direction of the main suspect in the case. Marie liked to flirt, in part, to piss off her boyfriend, Emile Gourbin. Marie was murdered at midnight, and there were no signs of a break-in. Gourbin was jealous, and because he and Marie were dating, Marie wouldn't have hesitated to let him into her house late at night.
When police questioned Gourbin, he smoothly produced a big group of friends who could verify his whereabouts at exactly the time Marie was murdered. They had spent the entire evening together, eating, drinking, playing cards, and going to bed at one in the morning. Police were still suspicious, and their suspicions grew when they scraped under Gourbin's nails and found what looked like skin tissue. At the time they were decades away from any biological test which could link the skin cells under Gourbin's nails to Marie. There was no way to analyse the tissue.
Until a closer look produced a new avenue of evidence. The tissue was covered in powder. The powder included magnesium stearate, a white powder commonly used as a binding agent, zinc oxide, a sunscreen, bismuth, an iridescent mineral used to make glittering powders, and a red iron-oxide. It was face powder. And, according to the chemist in Lyons, he only mixed it for Marie Latelle.
When Gourbin realised that, due to poor hand-washing habits, he was going to be convicted of murder, he spilled the whole plan. He had met his friends, and they had dined together, but that dinner was heavy on the drinking and light on the eating. After his friends got drunk enough, he'd set the clock ahead. They'd been drunk enough to be staggering and sleepy long before midnight, but believed that they had stayed up until one. Once they were gone, Gourbin had gone out and murdered Marie.
And he'd have gotten away with it, too, if he'd just used a nail brush.