Jamie Spencer brought attention to an interesting post by West Palm Beach criminal lawyer, Ron Chapman. Ron was lamenting that experienced prosecutors often cut their nose to spite their face by dismissing substantiated claims by a defense lawyer their client is innocent. Ron spoke of his personal experience representing a man charged with assaulting his wife by cutting her with a knife. A forensic pathology examination showed the wounds on the wife were self-inflicted. The prosecutors summarily dismissed this evidence. At trial, Ron's client was acquitted and the jury inquired why the case hadn't been dumped long before trial. Jamie surmised the prosecutors gave little credence to the defense expert because he was a hired gun. Since the hired gun was paid for his expertise, in the prosecutor's eyes, he must be lying.
I don't think prosecutors are that sophisticated. I think they just don't trust the defense on issues they've already made up their mind about. I've worked with prosecutors who, unbelievably, insisted police officers never lied or shaded their reports to support their theory of a case. They argued "why would a police officer risk his career to nail my client with a lie or prevarication?" The answer is simple, of course. Police officers are human beings and they like being right. They don't want their mistaken judgment discovered since it's embarrassing to be exposed in this way.
But back to the question whether a paid expert is less credible in the eyes of the prosecutor. Well, maybe. But the important folks to worry about are the jury. And it seemed Ron Chapman made the right call to press his case to trial and convince the people who really mattered that his client was falsely accused.