If the case depends upon scientific evidence, such as DNA, blood type, explosives residue, tire marks or fingerprints, it will be important to try to obtain all the reports prepared by prosecution experts and to evaluate what test or experts the defense should seek on behalf of the client's defense. The lawyer may need to obtain the actual evidence and ask an expert to retest it, or the lawyer may only want the expert to assist in understanding the weaknesses in the prosecution's expert's examination. For example, if the prosecution expert determined that there was blood on the defendant's shirt that matched the blood of the victim and made that determination by using a method that is unreliable, defense counsel may want to have an expert point out the unreliability of the testing procedure rather than retest the blood stain. If the prosecution destroyed all of the evidence during the testing procedure, it will be essential to have an expert help point out the weaknesses in the testing. If the court denies funding for an expert, counsel will need to explain why that decision hurts the defense. Getting experts for the defense may be very difficult but if the lawyer is going to get court authorization for any of the above, the lawyer will have to be fully prepared to justify the need. The above preparation and analysis will promote the reasoning and application to the court. If no expert can be retained, defense counsel will need to do research to find books or other publications that might help make the case to get an expert, or to impeach the prosecution case even without expert assistance. There is a wealth of good, reliable information available on the internet which will assist with the understanding of the scientific issues in the case.
See also Evidence