First off, you claimed that the report was a forensic analysis. It isn't. It is forensic psychology (profiling).
Second, you claimed that The Profiling Project was part of the university. It isn't. It is independent and funded solely by one man with an obvious agenda.
Third, the report that produced has been criticized as garbage for a whole host of reasons.
Fourth, we do not know that the casings were cleaned up. As one of my links very nicely pointed out, if a revolver was used, there would be no casings. Otherwise, casings are small and round, they roll. They are also not always found. This is not a crime scene from a television drama.
Fifth, you claim that Seth Rich was the source of the DNC email leak. There is no evidence of this. In fact, the emails that the conservative propagandists claim he leaked are the same ones that the government has alleged Russia hacked.
Sixth, if this was a "professional hit," the supposed assassin made a mess of it. If you were a professional trying to kill someone, why would your shoot him in the spine? The head or chest makes more sense.
Seventh, the police are thinking failed robbery because of other similar incidents in the area. Maybe the wallet was still there because he robber got spooked, heard sirens, someone walked by, who knows.