Fred and Rose West came to light in the 90s but were active for years and years. Before everyone had a mobile some young women just disappeared and the police didn’t seem to think much of it.
Levi Bellfield - yes, he just went around hitting women over the head with a hammer around South West London and the police didn’t seem to see a link.
In the Ipswich case it all happened very quickly over a few days.
There was Joanna Dennehy who killed three men in a ten day spree.
Then there are things like the IS terror attacks where a lot of people were killed or injured very quickly at random.
And Lucy Letby, Harold Shipman - medical killers.
We don’t know if there are other serial killers out there who just haven’t been caught yet because people do still go missing.
Computers and DNA have made catching people easier but there are still a lot of unsolved cases. At least it’s not a case of knowing there is someone out there regularly attacking women and the police simply saying don’t go out in the dark - pretty impossible for most of us.