Vicarious liability and such

[jonathan]

So I just finished re-reading American Brutus, and I ran across something in particular that confused me. For a while now, I've been going on the idea that the co-conspirators were charged with murder even if they believed that the plan was still only to kidnap. In Blood on the Moon, Ed Steers goes into this a little bit, but I believe these lines (page 210, paperback) sum up his point…

"Most important to the case of the Lincoln conspirators, a person may be a member of an unlawful conspiracy without knowing all of the details of the conspiracy or even all of the other members."

and

"The law further states that when a felony is committed in pursuance of a conspiracy that had as it's design only a misdemeanor, the misdemeanor becomes merged into the felony."

But now, reading AB (page 364, paperback), Kauffman says this…

"The defense rested in mid-June, and began their closing arguments shortly afterward. They conceded that by the laws of conspiracy, the act of one participant transfers guilt to all. But that holds true only when it is the same act that they had conspired to do. Since the defendants had engaged in a conspiracy to capture the president, they could not be held responsible for Booth's last minute change in the plan.

There seems to be a contradiction on the point of whether or not the defendants could legally be charged with murder. It seems like this would be a matter of fact, not opinion. Is Kauffman simply pointing out the strategy that the defense was using? Because it sounds as if he's stating a fact. Which is correct? What am I missing here? If something obvious has completely gone over my head, please let me down easy.