A Grand Jury can be made up of the nuttiest, most biased idiots willing to serve. Remember the defense is not represented in a Grand Jury and has no say in who is seated as part of that Grand Jury. It is supposed to be a random cross section of people and therefore the average IQ in a grand jury will be about that of the general public and that is pretty scary.
In today’s world of meta data, there are records on almost all of us that tell what we think and say.
Those can be used as tools in jury selection.