"And, just what would the strangers motive be? There was no plea for money, there was no robbery, her purse, wallet etc. were still at home. Usually there is a reason to murder someone. So, the stranger had to drive 90 miles & have access to a boat, just to set up Scott, but why?"
If you're asking me why a stranger who murdered Laci Peterson would have taken the effort to dump her body where Scott Peterson said he was fishing, I've already answered in Post 301: to divert suspicion to another suspect and get away with the crime. It does not require of that murderer any personal hatred of Scott Peterson. It simply requires not giving a damn about Scott Peterson's fate for an alternative murderer of Laci to frame her husband and divert suspicion away from oneself.
As to why someone other than Scott Peterson would murder Laci Peterson? One can only speculate about motives ranging from convenience to pathological.
Do a Google search on "serial killer" and spend ten minutes reading through the results.
I see; so you want us to SPECULATE on why somebody else would murder Laci -- even though there is not ONE SHRED of evidence to back that up -- but you don't want the jury to DEDUCE that Scott was the person who murdered her in spite of the facts that give support to that very theory.
I think you are Mark Geragos and these rantings are your unused defense notes.