Crimes occur with many participants. Murders, car-jacking, embezzlement, fraud, white collar crime, insurance fraud, and almost any crime you can imagine can happen with more than one defendant. Anytime there is a case involving multiple defendants there is the possibility that one of the defendants will turn “state’s evidence”. In other words, one defendant works out a deal with the District Attorney or United States Attorney for a lesser sentence, lesser charges, or even a complete dismissal in return for testifying against the remaining defendants.
What should the defense attorney do who is faced with the co-defendant who is now cooperating with the prosecutor? Of course, the first thing the prosecutor will do is require the cooperating defendant to “tell the truth, the whole truth and nothing but the truth, no matter who is asking the questions”. The “truth” is an elusive term. Ideally, it means that the testifying co-defendant will, in fact, reveal all to the jury and to anyone who asks the questions.
In reality, for the prosecutor the “truth” means testify to the same statement that the cooperating defendant gave when arrested. When looking to give a deal to one or more defendants, one of the most desirable qualities is that the statement given when arrested is the one the prosecutor wants to use as the “truth” of the case. Then when the testimony is given it is consistent with the earlier statement and makes it easy for the prosecutor to argue to the jury that testimony is the same as the earlier statement and thus is “truthful” since when the first statement was made there wasn’t anything promised in return.