Lye

Sodium hydroxide, aka lye, is an alkaline substance used in drain cleaning, soap-making, and the production of pretzels. This highly caustic product can also be deployed upon human or animal tissues to render them down into a liquid. During the 1930s, Italian serial killer Leonarda Cianciulli used lye to turn the bodies of three murdered women into soap. The fact that we know about her crimes means that she must've eventually come clean.