Agree with a lot of what has been said here. A friend was brutally raped by a man she knew (but was not involved with in any way). He strangled her and left her for dead but she was playing possum, called the cops. They got him a few days later. Ran his DNA and it showed he was responsible for 3 other child rapes and one child rape/murder. He was already out on parole for a child attempted kidnapping. At his trial the judge allowed, in the sentencing phase, women to come forward who had been molested by him starting when he was 12. This evidence was sealed at the trial. He got life without parole. This one monster has done horrible things to a dozen woman, that we know of.
The police were supposed to be watching him, they were not. He was violating every part of his parole, including living with a woman with a child. His car trunk contained a book with long lurid descriptions of sex crimes he wanted to commit. He had written it as part of his court ordered psychiatric treatment. Part of his parole was that he was supposed to give a DNA sample. He had avoided this for two years. The DNA sample was all that was needed to link him to the murder and other rapes.
What I saw in this case reinforces many of the comments made above.