Here are five common reasons mistrials occur:

Juror misconduct.
Jurors were improperly selected.
Inadmissible evidence.
A key trial participant is unavailable.
The jury cannot reach a unanimous verdict (often referred to as “hung jury.”

1.- Juror Misconduct

Jurors receive specific instructions from the presiding judge on what they can and cannot do while serving on the jury. These instructions can include not discussing the case or the evidence with anyone, not reading news about the case, including social media, or not watching television. Sometimes, in high-profile cases, the court can sequester the jury to protect them from improper influence. Other rules include not speaking to attorneys.

Having contact with one of the parties or witnesses, considering evidence not presented in the trial, or conducting an independent investigation of the matter are all examples of juror misconduct.

If it comes to light that a juror violated the court’s rules, the presiding judge may declare a mistrial.

2.-Jury Improperly Selected

Prosecution and defense attorneys help the court select jurors through the voir dire process. The purpose of voir dire is to question the jurors to determine whether they are competent and able to decide the case fairly and impartially.

Generally, the attorneys and the court seek jurors who do not know the case, the parties, or the witnesses involved.

There may be a mistrial if a judge determines that the lawyers used improper factors in selecting jury members or that a juror lied during the voir dire process.

3.-Jury Hears Inadmissible Evidence

A jury should only hear evidence that is admissible under the applicable rules of evidence. Sometimes, jurors become exposed to inadmissible evidence (evidence that does not comport with the rules). Other times, the lawyers make improper statements in the presence of the jury. If the evidence or improper statements are severe enough to taint the case, the presiding judge will declare a mistrial.

4.- A Key Trial Participant Is Unavailable

When a key figure in the trial – such as a juror, witness, or attorney – becomes unavailable, the judge may have no choice but to declare a mistrial. Extraordinary circumstances, such as the death or illness of a necessary participant, or some other cause, can cause a mistrial.

At this point, the primary risk of a mistrial in the Holmes case is that the number of available jurors falls below 12. The case started with 17 jurors: 12 jurors and five alternates.

Three jurors have asked Judge Davila to relieve them of their duties, and the Judge has dismissed two of them. Judge Davila just dismissed another juror caught playing Sudoku during the trial proceedings. Only two alternates remain. We are in the middle of a pandemic, and the threat of COVID-19 affecting the trial proceedings is real. Early on in the Holmes trial, Judge Davila had to cancel a court session after a juror was exposed to COVID-19.

5.-Hung Jury/Lack of Unanimous Verdict

A deadlocked jury is a common reason for declaring a mistrial when the jurors cannot agree over the defendant’s guilt or innocence.

Once the prosecution and the defense teams have presented their evidence and closing arguments in a federal criminal trial, the judge provides the jury with the instructions to follow to decide the case. Next, the jury retires to weigh all of the evidence and render a verdict privately.

Federal criminal courts require a unanimous verdict. (As noted above, almost every state also requires that the jury in a criminal trial reach a unanimous verdict.)

When a jury cannot reach a unanimous decision, the presiding judge will declare a mistrial.

Sometimes, when a jury informs the judge that it is deadlocked, the presiding judge will often instruct the jury to continue deliberating further to see if they can reach a unanimous verdict with the benefit of more time and discussion. Or, the presiding judge may allow the jury to present a list of questions for the parties involved to answer. When additional time or more information does not lead to a unanimous verdict, the judge has no choice but to declare a mistrial.


Elizabeth Holmes trial observers fear that the court is running out of available jurors, and there are many weeks of trial left to go. Only two alternate jurors remain. Therefore, the jury is the biggest threat to the trial reaching its conclusion.