I don't doubt that RFK was having Marilyn watched by private detectives, and I strongly suspect that someone scoured her home for possibly embarrassing material before the police arrived on the scene.
On the other hand, just because her doctor gave her a 60 pill prescription, this doesn't tell me that Marilyn was being set up for suicide. Such large prescriptions weren't uncommon back then.
As another poster recalls, there were no pills found in Marilyn's mouth or stomach. (Neither, I believe, were any found in Anna Nicole's stomach.) This doesn't necessarily mean that drugs were administered by needle or suppository. It could just mean that the women died of an adverse reaction to the drugs some time after ingesting them. Their respiration became depressed, and eventually ceased.
The problem I have with a murder plot is that it would involve silencing a woman generally considered a drug-addled bimbo -- and therefore without credibility -- in favor of conspiring with people like her psychiatrist, etc., who had some credibility, and would potentially be dangerous witnesses.
It would have been easier to have Marilyn committed to a mental institution, if she was considered that much of a threat.
Her fatal dose was administered by a fLeets enema. Read "Goddess" which came out in the 70s or early 80s. Absolute, direct link to RFK.