This is true for serial killers in general though. Murders tend to be premeditated. If you are planning a murder you’ll look for ways to maximize your success and minimize the chance of getting caught. In modern times you don’t have to rely on pure strength; there’s a plethora of workarounds from drugs to guns. The actual desire to end a human life (usual enabled by some form of psychopathy) is the limiting factor. A serial killer personality type doesn’t throw the towel just because they are physically weak.