An initial strategy used by criminal defense lawyers is searching for errors by law enforcement officials involved with the case. There could have been irregularities with how physical evidence was managed, for example. A police officer might even have done something illegal.
When a defense lawyer finds these types of problems, the details can be presented to the prosecution with a request to drop the charges. If that effort is unsuccessful, the lawyer may wait until a court hearing to convince the judge to dismiss the case. These are often the most positive possible outcomes for defendants.
Sometimes lawyers discover that a search might have been conducted inappropriately. For instance, police need a warrant issued by a judge to legally search a suspect's home. They also are allowed to do this with the occupant's consent, but might not without proof of consent. Police are well aware that a case can be dismissed if a search is conducted without a warrant.
Nevertheless, some irregularities may be evident. If the officers broke into the home, the defense lawyer wants to know how long they waited after knocking and announcing their arrival. If nobody was home at the time, the lawyer must find witnesses who remember the incident. Police must announce their presence and wait a reasonable amount of time for someone to reach the door.
Law enforcement officials are required to read the Miranda Rights to a suspect they arrest and plan to question. The requirement only applies to questioning, not to the arrest itself. The officials must immediately stop asking questions as soon as the defendant requests an attorney. Defense lawyers learn whether this procedure was followed properly.
Technical problems can occur in forensic labs and during the process known as the chain of evidence or chain of custody. Any indication of mishandling or potential contamination can be used by a defense attorney to have a case dismissed. For instance, if documentation of physical evidence is missing any part of the time frame, that evidence may no longer be valid. Nobody can verify where it was for a certain length of time.
In some instances, inappropriate behavior by law enforcement is not discovered until the trial has begun. For that reason, defense attorneys continue seeking evidence of problems with police behavior and forensic procedures. This does not stop until the case is over.