A grand jury's job is very different than that of a trial, or "petit" (small) jury. The grand jury determines whether there is enough evidence to warrant sending the case to trial -- whether there's "probable cause" to conclude that a particular person comitted a crime. A trial jury, on the other hand, decides actual guilt and sometimes punishment. One consequence of this difference is that grand juries can consider evidence that would otherwise be excluded at trial, such as evidence obtained in violation of the Fourth Amendment's prohibition against unreasonable searches and seizures. Similarly, a grand jury can consider hearsay evidence (evidence offered by someone who did not have personal experience with the subject matter of the testimony).