It wasn’t planted. The “magic bullet” wasn’t pristine. It was deformed (laterally flattened), and behaved precisely as you would expect if it went through JFK’s throat without hitting bone, and then was slowed down and tumbling when it exited JFK and hit Connolly.
A tumbling, slowed bullet would deform just like that if it hit Connolly’s ribs sideways. Connolly’s back entry wound indicates this.
Posner did a better job explaining this than I could, but I found it convincing.
Also, the killshot from the Zapruder film was fired from the front, and was not from a 6.5 Carcano.
Reading the Posner book made me a firm skeptic of the conspiracy theories where previously I had been mostly neutral. One of the clinchers for me is the fact that the conspiracy theories were first promoted by the left.