Remember that the evidence presented by the prosecution to a grand jury is often highly skewed and the defense seldom shows its hand right off.
More than once a grand jury member has said, ‘if we had known that, we wouldn’t have charged……’

Remember your Miranda rights, “…..anything you say can and will be used against you in a court of law…..”
It says nothing about being used in your defense.
Its why defense attorneys subpoena any and all evidence in a case, the prosecution has no legal reason to present anything detrimental to their case.