If she had her hands all over that tray full of surgical stuff, where did her fingerprints go and all the blood that would have splattered on her clothing
And why was no other evidence found she was even in the room
John mentioned the blood to Marty once, but didn't say anything out loud about it to Bo so the two of them arresting Marty is just absurd! They must know they need evidence. Didn't david just give them a false confession and now two, same murder! jeez, they'll be lucky not to both be fired.