This isn’t surprising in the least. If I can remember correctly I read somewhere that the FBI has said that at any given time there are something like 10 active serial killers in the US, probably more. There are many more intermittently active serial killers than that. There’s probably been 10 times as many serial killers come and gone, since the term existed, that we’ll never know about because they got away with their crimes and were never caught. Reality can be a real b!tch sometimes.
A police officer friend of mine told me once that they only catch the dumb ones. The more intelligent criminals rarely get caught.