Getting to potentially important defense witnesses before police or federal investigators will almost always make or break your defense. Witnesses have a way of being intimidated by police and investigators to side with the prosecution. Therefore, it is absolutely crucial to get statements from these witnesses before they are corrupted by the other side. A good investigation can more often than not result in finding a key alibi witness, or establishing that a potential eyewitness identification has fatal weaknesses. With a good investigation, you can prepare your case for trial from a position of strength and confidence rather than eyewitness misidentification weakness and uncertainty.
A carefully planned and proper defense investigation in a criminal case 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 reasonable doubt among the jurors as to the client’s guilt. The evidence may show that the client is guilty, but of a lessor 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.
from http://www.CriminalDefenseLawyer.com (June 9, 2003)
Eyewitness misidentification is the single greatest cause of wrongful convictions nationwide, playing a role in more than 75% of convictions overturned through DNA testing.
While eyewitness testimony can be persuasive evidence before a judge or jury, 30 years of strong social science research has proven that eyewitness identification is often unreliable. Research shows that the human mind is not like a tape recorder; we neither record events exactly as we see them, nor recall them like a tape that has been rewound. Instead, witness memory is like any other evidence at a crime scene; it must be preserved carefully and retrieved methodically, or it can be contaminated.