The rule of thumb with Grand Juries is “The prosecutor can get them [the Grand Jury] to indict a ham sandwich.”
It only seems this way because of case loads, prosecutors generally don’t bring in half-assed cases, they bring in the ones that they believe they can successfully prosecute based on the evidence.
I think the complete quote is “Any decent prosecuter can get a grand jury to indict a ham sandwich on the death of the pig”.