The most important testimony in any criminal matter, whether at the grand jury or trial stage, is the testimony of the potential target of the investigation (or the defendant, if the case goes to trial). Clearly, this was true in the grand jury investigation of the shooting death of Michael Brown. Officer Darren Wilson’s testimony was critical to the decision not to indict.
Some critics of that decision find fault with the fact that Wilson’s lengthy account of what happened went essentially unchallenged by prosecutors. Some wonder why he testified at all, since targets in the vast majority of criminal investigations do not testify before the grand jury.
In fact, it is standard operating procedure to permit a potential target to testify in the grand jury if he wishes to do so.
Most, of course, do not. The vast majority of cases presented before the grand jury involve defendants who are clearly guilty (indeed, many of them have already confessed to police while being interviewed immediately after the incident being investigated). Because witnesses are not permitted to have their lawyers with them in the grand jury, they do not want to testify in a setting where anything they say can be used against them.
Nevertheless, investigative targets who are actually innocent – or who at least believe they can convince people of their innocence – often want to testify in order to try to persuade the grand jury not to charge them. In federal cases, prosecutors are instructed by the U.S. Attorney’s Manual (Sec. 9-11.152) to look on such requests favorably.
Those who wonder why Wilson’s account was not challenged by the prosecutors misunderstand the purpose of grand jury proceedings. At this preliminary stage, the prosecutor is not trying to win a conviction – he is trying to decide whether there is a case worth indicting. Moreover, if it appears the prosecutor is not being aggressive enough, or is missing something that should be asked, the grand jurors themselves are permitted to ask questions directly – or at least demand that the prosecutor ask those questions. (This is a big difference from trial, at which the jury does not get to ask questions, must rely on the lawyers, and can often be frustrated by what they perceive as the lawyers’ failure to press the witness about this or that point.)
With this understanding, it is easy to see why an investigative target’s account will often not be challenged by the prosecutor at the grand jury stage. On the one hand, if it appears the target is telling the truth (because his version of events matches up with the forensics and testimony of other witnesses), there is no reason to challenge his testimony.
On the other hand, if the prosecutor believes the target is lying to the grand jury, then the high likelihood is that the prosecutor will become convinced of the target’s guilt and the decision will be made to indict him. In that situation, there is no reason to preview the cross-examination the prosecutor would do at the trial – that will only help the target and his lawyer prepare to meet it later on. The prosecutor would rather let the target keep lying because those lies will help the case down the road. The lies, moreover, are unlikely to confuse the grand jury; having heard all the evidence, the grand jurors, like the prosecutor, will know the target is lying. And if the grand jurors are confused, they can ask clarifying questions, or the prosecutor can later remind them of the evidence that shows the target has lied.
For a prosecutor, the point of the grand jury is to make sure (a) you don’t bring cases you shouldn’t bring, and (b) you improve your chances of winning the cases you should bring – at the only stage where winning matters, the eventual trial. You can’t win a case in the grand jury, any more than you can win the World Series in spring training.