Jesus, "a dog with a bone," as Mark Urik said about someone not long ago. Apparently you simply cannot admit you are wrong and let it go. I am on the verge of suffering not merely "Sandy Larsen flashbacks" but "Sandy Larsen PTSD."
Look, booby, you cited (1) the Manson case, which was tried as a conspiracy case, and in fact the Tate and LaBianca murders were committed in the same manner by the same people on two successive nights, and (2) the OJ case, where the two murders were committed at the same time and place using the same weapon and obviously by the same perpetrator. Neither is the situation with JFK and Tippit.
Yes, obviously, crimes including murders are often tried together. This is why EVERY STATE has a statute or rule that crimes may be tried together if they are part of the "same criminal episode" (or words to that effect). DUH, YES? Likewise, EVERY STATE has a statute or rule that the crimes may be SEVERED, meaning SEPARATE TRIALS, if the defendant can show a single trial would result in unfair prejudice. DUH, YES? The very existence of these rules refutes the silly arguments you keep making. DUH, YES?
Because you are an "everything is black and white" know-it-all who has no clue how lawyers think - just like Sandy Larsen! - you seemingly can't grasp that every situation is different. What the hell was your career - IRS tax auditor? It can't have been anything requiring nuanced thinking.
Sometimes the prosecution would want separate trials, sometimes the defense would want one. Sometimes the prosecution would want one, the defense two. Often neither side cares one way or the other. It's always a matter of trial strategy. A simple Google search will generate multiple appellate cases where severance was an issue, with a defendant typically arguing that severance should have been granted and he was prejudiced because it was not.
For the last time: The JFK and Tippit murders are not inevitably connected, except in the mind of an LN zealot. The evidence and witnesses would be entirely different. There would be HUGE risk that a jury would connect the two and decide that Oswald "must have" killed Tippit if he killed JFK or "must have" killed JFK if he killed Tippit. This is the potential prejudice of trying both murders together, and it is precisely the invalid connection that Bugliosi made in the mock trial (where there obviously was not going to be a motion for severance because it was just a TV show).
I can GUARANTEE you that in a trial of Oswald the defense would be arguing both that (1) two trials were required because the murders were not part of the same episode, and (2) even if they were, severance should be granted because of the potential prejudice of trying them together. If the motion were denied, the defense would pursue what is called an interlocutory appeal, meaning an appeal before the trial even begins. If the interlocutory appeal were denied, the defense would preserve the severance issue as a major one on post-trial appeal. The correctness of the defense's position would be so clear in this case that I strongly doubt the prosecution would even oppose severance.
Apparently every forum has its Pretend Lawyers. At the Ed Forum, I not only had goofy Sandy, who was some sort of civil engineer, but even Jim DiEugenio lecturing me as to how I didn't understand the rules of evidence. Yeeesh ...