Grand juries indict in >99% of cases. It's just a rubber-stamp. The grand jury only hears the prosecutor's side. They can say pretty much anything. Please find me a case where a prosecutor or LEO was charged with perjury for lying to a grand jury.
I've been indicted twice and both times the grand jury transcripts were just lies.
In fact, I got someone released after 16 months in jail on a burglary charge because their grand jury was lies. The story the cop told was a complete fabrication.