All your questions are relevant and have actually been discussed. The problem is, those kind of leads (evidence of pizza gang in the MH, etc) were not pursued by police. They had hairs,prints, etc they found, but since they weren't DW's the police made no further attempts to link them to anyone else.
You can get verification of this by going back through the threads on the DW trial.
The regular posters on here (RHEO,FRESNODA,JOHN JAMIESON) are a wonderful source of LINKS to tons of information on the case. JUSt ask any one of us for specifics and we will do our best to point you to that information.
Remember it was LADY Macbeth who is famous for saying, "Out, OUT, Damnedd Spot!"