Pre-trial motions are an expected part of most criminal cases that go far in court. In California, pre-trial motions are typically filed after the preliminary hearing but before the case goes to trial. Usually, the defense attorney and the prosecutor appear in criminal court and make arguments that the case should be dismissed or that certain testimony or evidence should not be admitted at trial.
Most criminal cases are settled by means of a plea bargain, a dismissal or another order; therefore, they do not make it to pre-trial motions. In these cases, the preliminary hearing or arraignment is the last time the defendant will be in court.
For those cases that do make it to pre-trial motions, they will often be filed by both the prosecution and defense to address a few different issues. The parties will argue in their motions about what testimony and physical evidence can be used at trial, what legal arguments are allowed and whether there is any reason the defendant should not stand trial. The defense might argue, for example, that evidence obtained via illegal search be excluded or that a confession be excluded due to a failure to provide proper Miranda warnings.
The defense might argue in a DUI case that blood alcohol concentration test results should be kept out of trial because of procedural or mechanical deficiencies during testing. In a case where an individual has been charged with drunk driving, an attorney with experience in criminal defense might be able to help by putting forth an alternative theory of the event or arguing against the admissibility of prosecution evidence. An attorney might be able to negotiate a plea bargain before trial or challenge jurors during jury selection.