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DAVID CLARK
Criminal Defense Attorney

Expert Witnesses in Philadelphia DUI Cases

During the prosecution of DUI cases in Philadelphia, the role of expert witnesses consists of calling a doctor to indicate what, if any, blood and/or alcohol was found within a person’s system at the time of driving.

The Commonwealth or District Attorney’s office calls such a witness in order to prove that at the time of driving, a person was either A) above the legal limit of .08 blood alcohol content in a person’s system or under the influence of drugs or alcohol that may cause a person to be unable to operate a motor vehicle safely on the streets of Philadelphia.The commonwealth uses such witnesses to meet their burden of proof by calling those witnesses to analyze what was taken from the person at the time of the blood draw and/or the time the breathalyzer machine was administered.

The witness is called B) to show what effects, if any, it had on the person’s driving at the time.

Defense-Side Experts in Philadelphia DUI Cases

In Philadelphia, DUI cases can often be defended by calling DUI defense experts to the stand also. Especially in blood alcohol cases involving lower levels of alcohol in the system, a DUI expert can explain to a judge or jury that the amount of alcohol in a person’s system did not render that person unable to drive a motor vehicle safely on the roads of Philadelphia.

Because Philadelphia strictly adheres to the rules that anything above .08 or any controlled substance amount in a person’s system is per se DUI, an expert witness for the defense can try to negate some of those elements.

For instance, an expert for the defense can attack the way the blood was drawn from an individual, attacking whether or not the chain of custody has been maintained. Or a defense witness can attack whether a breathalyzer machine was maintained and/or used in a proper fashion when the test was given to an individual alleged to have been DUI at the time.

Expert Witnesses at DUI Trials in Philadelphia

In a DUI trial in Philadelphia, experts for both sides are given a significant amount of weight. The expert’s testimony would consist of the Commonwealth calling an expert to defend their position. That is, a person was unable to drive a motor vehicle safely on the streets of Philadelphia because they were either over the .08 blood alcohol content in their system or they had some number of controlled substance, often referred to as nanograms, in their system at the time of driving.

With those two elements, their expert would testify that based upon the laws of Pennsylvania, in their own opinion, that a person was unable to operate a motor vehicle safely on the streets of Philadelphia. The defense would then call their witness, should one exist, to rebut the Commonwealth’s case or the Commonwealth’s own witness testimony.

The defense witness can challenge a number of things. The way the blood was drawn (there are certain standards that have to be met), the accuracy of the test, and the accuracy of the breathalyzer machine. All of those can come in to play and if believed, then the Commonwealth will not be able to meet its burden of guilt beyond the reasonable doubt. And an individual with an experienced Philadelphia DUI attorney on their side can then end up in an acquittal which would have otherwise been a guilty verdict in any other jurisdiction.