Sometimes it is a newly trained officer with very little experience in testifying. Other times, it might be a cop who has been around for a while but he just hasn't handled very many DWI trials. The plain truth is that many DWI cases result in plea bargains, so an officer may handle dozens of arrests without ever actually being forced to testify in open Court.
These officers can easily be identified by an experienced attorney. Perhaps they have a high badge number, indicating a recent graduate. Or perhaps they work mornings/dayshift, when there will be only limited exposure to DWI enforcement in the field.
In our County, I would say that this is less likely to be an advantage with the Virginia State Police than it is with the County or other "agencies" (there are many "agencies" enforcing DWI these days). With less experienced officers, when an officer is reviewing a case prior to plea negotiations, they are sitting at a desk with the prosecutor, and they are reading from their notes. Once an officer takes the stand and is asked to testify from his memory, he might feel naked without his notes.
Most often, they take their notes to the stand and start looking at them as soon as they get questions, and it starts while their attorney (the prosecutor) is asking the questions! Defense objects to reading his notes, and, hopefully, it starts to unravel from there. We look for any inconsistencies and then we start asking about all of the other things that the officer can't remember.
"Let's go to the Videotape":
I'm always reminded of Sportscaster Warner Wolf, who used that line in every broadcast. Many attorneys don't even know that their officer has a video camera in his cruiser.
If you don't ask, they don't usually mention video, and they don't automatically bring the video evidence to help their case. Why? Because it doesn't always help their case! They would rather step up and tell a story, paint a picture, and fill it in with all of the details that are favorable to their version of the facts.
Very often, the video will show my client, appearing to be a good citizen, with his shirt tucked in, eyeglasses on straight, etc. My client will be interacting with the officer, having a normal conversation, following most of the instructions, asking questions, etc. Usually, both the audio and video are poor/amatuer quality, but that helps the defense.
In many cases, the officer will testify about what happened in the case, and then the tape will show something different.
Refusal of Breath Test:
Whenever the client is charged with Refusal, that creates another whole set of issues. Of course, the refusal itself may be a serious problem for the client, but the absence of a breath test is often very good news for defending the DWI charge.
Accidents cases are traditionally regarded as the more serious of the DWI cases, but an accident will often create many opportunities for the Defense. In most accident cases, the officer has not witnessed my client driving a car. Sometimes, there is no witness at all. They try to establish the element of "driving" by using admissions from the client, but that isn't always an option. If the client is transported to the hospital, there might not be a breath test, and blood tests open up another set of opportunities for the defense. If the officer has not witnessed the accident, then he might also be required to offer proof that the client has not been drinking since the accident.
Blood Tests Cases:
In Virginia, the law sets forth 3 circumstances when there should be a blood test instead of breath. The prosecution must prove, as a threshold issue, that one of these circumstances is present: Either the client is physically incapable of taking a breath test, or the breath test is unavailable, or the client is suspected of being under the influence of drugs or intoxicants other than alcohol. Then, if they have a valid reason for the blood test, they still have a long list of procedures that they must follow to obtain, preserve, and test the blood.