Why can't grand juries do it? I thought that it's when juries intentionally rule against what the law says, while saying otherwise, as a consequence of juries not being able to be penalized for their ruling. I don't seen any reason that the same can't happen with a grand jury.

A web search comes up with articles saying that it's more common with non-grand juries, but that's not the same as "cannot do it", while they also speak about a prosecutor's ability to re-indict, but that still doesn't guarantee them a charge.