Pretty irritating stuff.
And, in the grand scheme of things (no pun intended), what does it matter whether I believe the "official" version or I doubt it? Nobody cares (except perhaps my wife, when I yell at some smug talking head on TV...)
Have you read Case Open by Harold Weisberg? He refuted that work by Posner.
"Book Description
No one knows more about the assassination of President Kennedy than Harold Weisberg, so said the FBI in open court. Harold Weisberg - a former OSS and Senate Investigator-wrote and published Whitewash in 1965, the first book criticizing the conclusion of the Warren Commission. Since then, he has written and published seven books on President Kennedy's assassination. Case Open is a book Mr. Weisberg felt compelled to write. He felt a need and determination to set the record straight. In proving that Gerald Posner, in Case Closed, has proven nothing, Mr. Weisberg has proven that President Kennedy was killed by a conspiracy."
Continues at link to amazon.