From a research article:
Biologically speaking, Heydari et al. (2008) observed the most common biological characteristics of serial killers and noted that they have distinctive features like; face asymmetry, irregular ears sizes, either standing out or very small, irregular nose shape, and protruding lips.
And the reference is:
Heydari, E., Arzani, N., & Hassanzadeh, J. (2008). Mantle plume: the invisible serial killer— application to the Permian–Triassic boundary mass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology, 264(1), 147-162.