I don't have any good links, but in the US a grand jury does not deal with precrime. Juries are selected for a particular case. Grand juries are selected for

I don't have any good links, but in the US a grand jury does not deal with precrime. Juries are selected for a particular case. Grand juries are selected for a particular time period. During that time period potential cases will be brought before the grand jury who will then decide whether or not the case will go to trial (and if it does, a separate jury is selected for that case). I may be off on some details, but that is my understanding of how grand juries work.