Creative Speculation

Again this applies whether he was a patsy or the hit man.

Oswald had to know he was facing the death penalty. He also had to know, if he was part of a conspiracy, that his co-conspirators had left him to his own devices. As a patsy, Oswald would also have been highly motivated to provide what evidence he could to implicate the people that had worked to position him to take the fall.

Of course, if there were no co-conspirators, there would have been no one he could offer up to save his own skin.

This goes for Ruby, too. If Ruby was hired by the mob (or whoever) to silence Oswald, why did no one ever try to silence him? He was immediately captured. Bam, there goes the conspiracy, right back in the same place as before: their hired hit man being interrogated by the police. Why wouldn't they have tried to silence Ruby?