The police approached a person acting suspiciously in the vicinity of a murder. They were going to question him.
You don't "question" somebody by ordering him on his feet and attempting an illegal search. Looking "funny" to a shoe salesman does not constitute "probable cause".
All Oswald had to do was explain himself like the guy in the library did when the police descended on him.
Sure, blame the victim.
Unfortunately for Oswald, he couldn't do that because he was guilty.
There you go again, just assuming the thing you're supposed to be proving.
So he assaults a police officer
You have that backwards. The illegal search was an assault on Oswald. He was defending himself.
and gets taken in as a murder suspect due to his behavior.
What evidence did they have to arrest him for murder? Looking "funny" to a shoe salesman?
What you are suggesting is completely ludicrous. The DPD officers were searching for Tippit's killer. They had a general description.
The description that Postal gave the police dispatcher was
nothing like the description that the 10th and Patton witnesses gave. So why would the police consider this man a "suspect"?
They were not looking for or even had a clue who Lee Harvey Oswald was until after he is arrested. They were looking for a suspicious person in the area who might be the killer. That turned out to be Oswald. The subsequent investigation confirmed he was the murderer. Case closed. Excellent police work with the assistance of some astute citizens.
The subsequent investigation confirmed nothing of the kind. But even if it did, are you saying the ends justify the means? Civil rights exist for a reason.