Why is this important now? Because too often clients get into a case and don't understand how much it is going to really cost them. Then they get half-way through, and have trouble finishing the case successfully. You need to understand what you are facing before you start.
There are three main types of evidence: (a) testimony of facts from people who were witnesses, (b) physical evidence like objects or documents, (c) so-called "expert" testimony in which an expert testifies NOT about what happened in an individual case but how things work such as a machine or medical processes, or (like in the "CSI" TV shows) how that fiber sample in the car could only have come from the carpet in Joe's house.
Technically, an expert is required any time the testimony is an opinion, rather than an observation of fact. For example, I saw the light turn red is a fact. A car moving at 50 MPH with good brakes should be able to stop in X feet is an opinion requiring an expert to testify to his 'opinion.'
What is an 'expert?' Contrary to what you might think, an expert is not necessarily highly educated. A person without a high school education who has spent the last 10 years doing body work repairing damage to cars can be called as an expert -- based on real world experience -- as to the likely cost of repairing a car, what kind of damage was caused, etc. A person who spent 8 years running a dog kennel could testify that in her experienced opinion normal, healthy dogs don't react that way unless provoked by some cruelty.
For many criminal charges like DWI and reckless driving by speed, the prosecution depends upon the information from some kind of machine -- such as a radar gun, breathalyzer, etc. However, these machines are far from perfect. Sometimes they work correctly. Sometimes they don't. Sometimes they are used properly. Sometimes they are not. Anyone who has used any type of machinery or computer has experienced that they don't always work the way you want them to. Machines and devices are not always easy to use. And sometimes they produce improper results even when you do not notice any reason for that to happen.
However, the information provided by such machines may be the only or the primary evidence against you in a criminal trial. You are being accused by a machine!
Unfortunately, a lot of people are overly impressed with technology. Even though we should all know better, people tend to think that if a machine says it then it must be true. Our life experience should warn us of the opposite!
An expert witness can testify how these machines work, how often they don't work, and under what circumstances they don't work. They can explain to the jury what sometimes makes these machines give unreliable readings, and what is necessary to use them properly.
Therefore, an expert witness may be central and critical to your success in defending against criminal charges.
Hiring an expert wintess will be an additional expense. But this may be the key to removing criminal charges from your record, your future, and your life.
Your attorney will advise you when it is best to include an expert witness in your defense. It will be your decision whether or not to pay the added expense for an expert. However, your attorney may believe that he cannot win your case without the expert, and may warn you of this.
Unfortunately, it may often be necessary to hire an expert witness in time to testify at the trial.... although that might before you find out from the judge whether or not the judge will dismiss the charges or whether the prosecutor will strike a deal. There is often no other way to do this.
You may be required to notify the other side in any case months in advance of whom your expert witness(es) is (are) going to be. You might be blocked from using an expert witness if you did not announce them months in advance.