Presence of cut (possible concussion) , recent injuries to cheek, forearm, and wrist (all occurred at similar time according to science) AND robbery ?
"Recent" does not necessarily mean contemporaneous (i.e. during the same incident). Nor do those injuries - by themselves - confirm foul play. As I said, I have been present at a great many deaths where there were injuries that might give rise to such suspicions, but, were not at all a result of foul play that resulted in, or contributed to, the death.
And "robbery?" I suppose you meant to say, "theft." Robbery is a crime conducted through the use of force or fear..
Once again, I remind you, you cannot compel the police to investigate. And, even if they did investigate, you cannot compel them to act. If you want to take the bull by the horns and control any legal action, you would need to identify someone you have grounds to sue and then sue them.