Definition

A grand jury is an investigatory and an accusatory body in a criminal case; it does not include a determination of guilt and is not a preliminary hearing. A grand jury is secret, and the defense cannot cross-examine. The defense does not pose its case since the purpose is to determine if probable cause exists.

The jury consists of 12-23 jurors, depending upon the state. The jurors are drawn randomly from the population but are subject to voir dire. Hence, they may be selected from those drawn by the prosecution; the defense is not present.

The grand jury receives complaints and accusations, and it hears evidence brought by the state. It determines whether the probability of guilt exceeds probable cause:

• If it determines that the probability of responsibility exceeds probable cause, it returns a True Bill of indictment.

• If it determines that the probability of responsibility does not exceed probable cause, it returns No Bill.

There are very good reasons to use FactLogic in grand jury investigations. In 1983, the United States Supreme Court (Illinois v. Gates) defined the requirements to meet probable cause. Specifically, the decision said

• the totality of the circumstances are to be used,

• probable cause is to be viewed as a set of probabilities, and

• a deficiency in one probability can be compensated by the probability in another.
  

The requirements expressed by the United States Supreme Court have been implemented for the first time by FactLogic.

FactLogic helps each juror decide whether the probability of responsibility exceeds his idea of probable cause, and it justifies his decision, sparing him, the prosecutor, and the suspect the consequences of an inaccurate decision. Because FactLogic requires quantified judgments, statistical analysis is possible, and because a grand jury involves a relatively large number of jurors, their decisions can be determined with considerable accuracy. Of special interest to the prosecutor: FactLogic can predict the general verdict of a subsequent trial should the grand jury issue a True Bill. (See Criminal Case.) FactLogic also provides an excellent tool with which to conduct post-trial interviews.

The following two probabilities are particularly applicable to grand jurors:

• the probability of responsibility as determined from the facts by each juror and

• the probable cause as chosen by each juror.

Since FactLogic provides quantified decisions, statistical analysis can help the prosecutor reach a decision in any of five ways:

Carefully Define the Probability of Responsibility. FactLogic defines the probability of responsibility by computing the average and computing an interval on both sides of the average within which one can be 95% confident that the true probability of responsibility exists.

Compare the Probability of Responsibility to Probable Cause. FactLogic determines the probability that is exceeded, with 95% certainty, by the mean probability of responsibility. This probability should be compared to probable cause.

Compare the Probabilities of Responsibility for Two Suspects. FactLogic determines if the mean probability of responsibility for one suspect is significantly greater, with 95% certainty, than the mean for the other suspect.

Predict the General Verdict. FactLogic can use the probabilities from the grand jurors to predict the general verdict of a subsequent trial if a True Bill is returned.

Accept a True Bill. Analysis can determine the probability of erring by accepting either of the two True Bill decisions:

• The probability of issuing a True Bill when, in fact, the probability of responsibility does not exceed probable cause.

• The probability of not issuing a True Bill when, in fact, the probability of responsibility exceeds probable cause.

Summary

The U.S. Supreme Court implicitly recommends determining probable cause by the method implemented by FactLogic. Each grand juror can use FactLogic to determine the probability of responsibility and compare it to his idea of probable cause. The grand jury would return a True Bill if a majority of grand jurors believes the probability of responsibility exceeds probable cause. The relatively large number of grand jurors (i.e., 12-23) presents an excellent opportunity to use statistical analysis to:

• Carefully define the probability of responsibility.

• Compare the probability of responsibility to probable cause.

• Compare the probabilities of responsibility of multiple suspects.

• Predict the general verdict of a subsequent trial.

• Accept a True Bill.

FactLogic can also be used to conduct post-trial interviews.

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