I don't know if the implication in 'three cold cases near Boulder' is that the perpetrator of one of them may have 'graduated' to a more daring and notorious crime. Perhaps one could take 'three cold cases from Alaska' and be closer to the truth. I don't know.

To the extent that the statistics indicate a resident of the immediate neighborhood, perhaps some fairly nearby cases are indeed relevant. And if you expand 'resident of the neighborhood' both geographically and temporally, you get far more suspects. You even get the McReynolds who used to live three miles away years before the crime.

Standard police work would be to check the known perverts and then check the suspected perverts who had come to the attention of police in other cases but against whom a case had never been sufficiently established. Ofcourse, the BPD and the phrase 'standard police work' does seem strangely incompatible.