A carefully planned and proper criminal defense investigation can lead to a number of favorable results. The best result, of course, is proof that the client is innocent of the charge. That is the ultimate goal.
The next best result is evidence. The criminal defense investigator must look at developing evidence, which may create a reasonable doubt as to the client's guilt. The evidence may show that the client is guilty, but of a lesser degree of the crime charged. The defense investigation may also show that the client's constitutional rights were violated.
When conducting a criminal defense investigation, the investigator must be knowledgeable of police procedures, interview techniques, and, most of all, the investigator must be prompt. In most cases it is important that the investigator start the case as soon as possible after the charges are brought against the client. Things change in criminal cases and they can change quickly. The crime scene changes, physical facts change, the site of pertinent events change, or moves or is replaced. An object of importance may be discarded or destroyed. Witness may move or forget.
The investigator's role is not to counsel the client. The attorney would have advised him of his rights with regard to trial and the legal methods. The investigator must be very careful not to undermine what the attorney has said, and not to promise things which the attorney may not be able to deliver. That's why it is so important for the attorney and the investigator to work closely together so those prospective roles are clearly identified. The investigator must know what to say to the client and what not to say.