I agree that it would be smart for LE to look at people recently released from prison. But, if we assume that POI was a hired "hitman", and he couldn't find the people (or person) who he had been hired to eliminate, and killed the girls as a secondary option, then we must assume he recognized the girls. (or at least one of them) That brings me to this point: Not only would I look at people who had been released from prison, but I would look at people who had recently been released from prison that may have had reason to be around the families of the girls. Did any of that make sense? lol.
I tend to think that the overkill w/ the girls shows a lot about the mindset of the murderer. I think he was young and inexperienced in the world of murder. I do not think he was a "professional". He may have been involved in the drug world and had been around guns etc............. but, I do not think he had taken lives before the girls were shot. I could be Totally off base. But criminal profiling can provide a lot of (speculative) information about criminals. I think profiling and victimology can help LE a lot.
If you follow what a profiler would say, it would most likely be a young person, a female or a homosexual that would have committed the crimes. I hope that one day, we will know the truth.