BY JUDD LEGUM POSTED ON NOVEMBER 26, 2014 | Think Progress

On Monday, Prosecutor Bob McCulloch announced that a grand jury had decided not to indict Darren Wilson, the officer who killed Michael Brown. But that decision was the result of a process that turned the purpose of a grand jury on its head.

Justice Antonin Scalia, in the 1992 Supreme Court case of United States v. Williams, explained what the role of a grand jury has been for hundreds of years.

It is the grand jury’s function not ‘to enquire … upon what foundation [the charge may be] denied,’ or otherwise to try the suspect’s defenses, but only to examine ‘upon what foundation [the charge] is made’ by the prosecutor. Respublica v. Shaffer, 1 Dall. 236 (O. T. Phila. 1788); see also F. Wharton, Criminal Pleading and Practice § 360, pp. 248-249 (8th ed. 1880). As a consequence,neither in this country nor in England has the suspect under investigation by the grand jury ever been thought to have a right to testify or to have exculpatory evidence presented.

This passage was first highlighted by attorney Ian Samuel, a former clerk to Justice Scalia.

In contrast, McCulloch allowed Wilson to testify for hours before the grand jury and presented them with every scrap of exculpatory evidence available. In his press conference, McCulloch said that the grand jury did not indict because eyewitness testimony that established Wilson was acting in self-defense was contradicted by other exculpatory evidence. What McCulloch didn’t say is that he was under no obligation to present such evidence to the grand jury. The only reason one would present such evidence is to reduce the chances that the grand jury would indict Darren Wilson.

Compare Justice Scalia’s description of the role of the grand jury to what the prosecutors told the Ferguson grand jury before they started their deliberations:

And you must find probable cause to believe that Darren Wilson did not act in lawful self-defense and you must find probable cause to believe that Darren Wilson did not use lawful force in making an arrest. If you find those things, which is kind of like finding a negative, you cannot return an indictment on anything or true bill unless you find both of those things. Because both arecomplete defenses to any offense and they both have been raised in his, in the evidence.

As Justice Scalia explained the evidence to support these “complete defenses,” including Wilson’s testimony, was only included by McCulloch by ignoring how grand juries historically work.

There were several eyewitness accounts that strongly suggested Wilson did not act in self-defense. McCulloch could have, and his critics say should have, presented that evidence to the grand jury and likely returned an indictment in days, not months. It’s a low bar, which is why virtually all grand juries return indictments.

But McCulloch chose a different path.