The first rule of examining an expert witness like this is not to forget that you are not an expert. Don't get in a battle of wits with them, for two reason. One, you will lose. And two, you will end up giving the expert a chance to talk theory, science, process, and mathematical formulas. This is stuff he is really interested in and stuff you may be interested in, but the jury doesn't want to hear it.
Second, start with the basics. While you have the guy on the stand, go through the history of the machine with him. If he doesn't know it it will hurt his credibility. If he does know it, it will give some good information to the jury. Take this opportunity to discuss the process of designing the machine, which has included many changes, and some interesting test results.
Third, go for the maintenance records of that particular machine. One of the actual beneficial things about this machine is the data it keeps about itself and stores just waiting for you to take a look at it. As a DUI attorney in Seattle, this is just the information you are looking to take advantage of. What you will see if you take a look is a set of problems occurring around your client's test that were not able to be recreated or "fixed" necessarily. If the cause of the malfunction is a mystery, how can the machine be accurate?
Fourth, and finally, attack the database, which houses all of the information about the DataMaster. You can see error codes on the database and other information related to the inaccuracy or malfunction of the machine. Do a little digging and you'll be surprised at what you can find.
If you are charged with Seattle DUI, don't settle for a criminal lawyer that will just go through the motions. Get someone who will do some digging, who will fight for your case. It can mean the difference in conviction and dismissal.
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