If you get a chance to talk to the State’s expert witness before trial (if you’re allowed to, try; the best experts often see themselves as neutral, and will explain their conclusions to you), your last question should be: “What book should I read to learn about this topic myself.” Get the book; it’ll be a learned treatise that you can mine for cross-examination material.
In a Houston murder trial once, for example, after the prosecutor asked the medical examiner whether the knife wound could have been irregular because my client twisted the knife, and the doctor assented to that proposition, I had him read this portion of DiMaio and DiMaio’s Forensic Pathology (if you try — or aspire to try — murder cases, you need a good library of forensic pathology texts) to the jury in its entirety:
The most common reason for a large, irregular knife wound is movement of the victim as the weapon is withdrawn. Prosecutors, however, like to contend that this is due to the perpetrator twisting the knife in the body after stabbing the individual.
While we’re on the topic of expert witnesses …
The only way to cross-examine an expert witness about his conclusions is to know at least as much, if not more about the narrow subject of his testimony that hurts you than he does. The trick is to define that subject as narrowly as possible. It’s not possible for a lawyer to know as much about, say, pediatrics than a pediatrician, but it is possible (maybe later I’ll talk about how) for a lawyer to know as much about the significance of hymenal notches as the same expert.
If you’re not fairly certain that you know as much about your narrowly-defined subject than the expert, then you’re asking for trouble when you cross-examine him about his conclusions. Also, if you are fairly certain that you know as much about your narrowly-defined subject than the expert, then you’re still asking for trouble (because you might be wrong) but the trouble might turn out to be worthwhile.
There are lots of things an expert can be cross-examined on other than his conclusions. For example, the government’s experts can be harsh critics of the police investigation. If you can’t get up to speed on the subject matter, or if your own study convinces you that the expert reached inescapable conclusions from the available evidence, question him about the holes in the evidence made available to him (try to tap into his frustration at things not being done just right) or leave him alone.