You are apparently unaware that a review of Ruby's polygraph shows that
he arguably actually failed the question about whether he was involved in a conspiracy with Oswald. The HSCA polygraph experts stated the following in their report regarding the reaction to the question, "Did you assist Oswald in the assassination?":
In fact, the reactions to the preceding question--(Did you assist Oswald in the assassination?)--showed the largest valid GSR reaction in test series No. 1. In addition, there is a constant suppression of breathing and a rise in blood pressure at the time of this crucial relevant question. From this test, it appeared to the panel that Ruby was possibly lying when answering "no" to the question, "Did you assist Oswald in the assassination?" This is contrary to Herndon's opinion that Ruby was truthful when answering that question. (8 HSCA 217-218)
You are also apparently unaware that Ruby later admitted that his tale about shooting Oswald to spare Jackie a trial was false.
Your bizarre scenario requires one to believe that every DPD officer was in on the plot and that therefore it would have been an easy task to kill Oswald much earlier. But no one argues such a silly scenario. Most DPD officers were not in on the plot.
Also, when did the DPD allow Oswald to "freely talk to the press"? When was this? Not on this planet. The DPD allowed Oswald to have very little interaction with the press. All of his comments to the press combined lasted less than 3 minutes.
The DPD also, in clear violation of the law, refused Oswald the right to have an attorney present during his questioning. Gee, why was that?
The DPD also failed to record a single one of Oswald's numerous interrogation sessions. Gee, why was that? This was the most important, historic suspect ever in DPD custody, but they never managed to record a single one of his interrogations.
There's also the fact that Ruby clearly entered the basement with help from someone inside the basement. The tale that he strolled down the Main Street ramp was debunked years ago. Even the HSCA rejected it and acknowledged that someone on the inside let Ruby enter the basement.
Finally, lone-gunman theorists still have no credible innocent explanation for all of Ruby's numerous long-distance calls to Mafia contacts in the weeks leading up to the assassination.