The original purpose of the grand jury was to have a body that could review a case to determine if there was enough evidence to proceed. The grand jury met in secret and if they chose to no-bill a case, no one ever knew the case had ever been considered.
The grand jury's role was to act as a check on the state in its prosecution of citizens accused of breaking the law. Over the years the grand jury has become a de facto rubber stamp for prosecutors. If the District Attorney wanted a case indicted, it was. If he wanted a case to go away because it was too hot a potato, all he had to do was let the grand jury know it was okay to no-bill it.
But someone, in Houston, a grand jury actually decided to take matters into its own hands. The grand jury was convened to consider whether anyone did something untoward regarding HPD's batmobile breath test machines.
You see, Amanda Culbertson kind of embarrassed Pat Lykos and her minions when she pointed out to her superiors in the HPD Crime Lab that the breath test machines in the batmobiles weren't, shall we say, very accurate or reliable. Then, to make matters worse, Ms. Culbertson testified under subpoena in a case and repeated her assertions that the breath tests conducted in the vans weren't all they were cracked up to be.
In the process of conducting its investigation, the grand jurors made it known that prosecutors weren't welcome in the room. Needless to say, this did not go over very well with Ms. Lykos. The DA's office asked the court of appeals to order the grand jurors to let prosecutors into the room but the appellate court thanked Ms. Lykos for playing but that she was not getting into the room - even if she said "pretty please or I'll indict someone's mother."
It stands to reason that the grand jurors are taking a hard look at the conduct of the DA's office in this entire sordid affair. Maybe someone gets indicted. Maybe (probably) not. But, I think it reasonable to assume that the grand jury is not going to indict Ms. Culbertson on some trumped up charge of telling the truth on the witness stand even thought it makes it harder for the state to prosecute motorists for driving while intoxicated.
Ms. Lykos has apparently forgotten that her ethical duty as a prosecutor isn't to coerce pleas or obtain convictions - it is to do justice. And that's even if it means dismissing cases because the machines used by law enforcement can't be relied upon to do what they are supposed to do.
H/T Murray Newman