Take DNA research and evidence as an example.  Technology has so greatly improved in this area that it helps to create a more efficient and accurate criminal justice system.  One might say it puts the "justice" in criminal justice.  DNA extraction is a much more reliable, consistent process, allowing investigators to obtain DNA samples more often and more completely.  This both helps to secure a conviction, as it is typically very convincing evidence, and it helps to avoid wrongly convicting others based on circumstantial instead of physical evidence.  It has also helped to free dozens of people from prison who were wrongly convicted, once that technology improved to the point where a more accurate sample could be obtained.

We can add to this example new methods of preservation of evidence, more modern scientific methods of processing crime scenes, and laser and spectrometer analysis research that allows us to more accurately measure anything from ballistics to fiber evidence.

Based on all of this, I'd say scientific research plays a giant role in improving criminal justice.

I would say that one reason for this is the fact that advances in forensic sciences can be helpful to law enforcement.  As forensic science gets better, law enforcement officers can hope to solve more crimes.

Another reason would be more preventative.  If, for example, we had better methods of detection, we might be more likely to detect terrorists who are trying to bring various kinds of explosives into public places.

In general, then, science can be helpful to criminal justice professionals.  It can help prevent crimes and help to catch people who have already committed crimes.