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 Top 5 Reasons For A Mistrial 

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Michael Santos

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A mistrial occurs mainly when the jury cannot reach a unanimous verdict to convict or acquit a criminal defendant. 



With fears mounting about the possibility that Elizabeth Holmes’ criminal fraud trial could end in a mistrial, it’s a good time to review what is a mistrial, and the five common reasons mistrials can occur. 

Observers of the Holmes trial fear a mistrial because the pool of alternate jurors has dwindled, and the trial is only about halfway completed. 

The trial began with 17 jurors, including five alternates, selected from a pool of about 200 candidates. At this point, only two alternates remain. 


A criminal trial does not always end with a guilty or not guilty verdict. Sometimes the outcome is a mistrial.

A mistrial is a trial essentially deemed invalid due to an error in the proceedings or because the jury could not reach a consensus regarding the verdict. 

In order to convict or acquit a criminal defendant, federal criminal procedures demand a unanimous decision. (Most state courts also require a unanimous verdict in criminal cases.)

When a criminal trial ends in a guilty verdict, the defendant can appeal to the next highest court. 

When a criminal trial ends in a not guilty verdict, the prosecution cannot appeal. 

When a mistrial occurs, prosecutors have the right to bring a new trial. 

Depending on the nature of the case and the required resources, prosecutors may choose not to retry the defendant. They may reassess their chances of winning a conviction the second time around, and they may also attempt plea bargaining with the defendant.


Here are five common reasons mistrials occur:

  1. Juror misconduct.
  2. Jurors were improperly selected. 
  3. Inadmissible evidence.
  4. A key trial participant is unavailable.
  5. 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.

What happens if there are not at least 12 jurors to finish the trial?  

Unless both sides agree to proceed with less than 12 jurors, which is hard to imagine in the Holmes case, the Judge would have to declare a mistrial. 

In the first week, the Judge dismissed a juror after learning that her employer would not compensate her for the time away. Recently, the Judge dismissed another juror after she said that her Buddhist faith made her uncomfortable with the idea of possibly punishing Holmes. Her replacement revealed that she did not speak English well, but Judge Davila did not allow her to leave.

It is not easy to find 17 people who have never heard of Theranos or Elizabeth Holmes and can set aside three months to serve on the jury. To remain unbiased, the jury also must remain protected from any news coverage, which is difficult in high-profile cases. Indeed, Judge Davila asks the jurors each court session whether they have recently heard about Holmes or Theranos.

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.

Double jeopardy does not apply when there is a mistrial. Double jeopardy only applies to someone convicted of a crime. Once convicted, the prosecution cannot try the person for the same crime. Since a mistrial does not result in a conviction, prosecutors can take the case to trial again. 


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. 

If the number of jurors drops below 12, the Judge will likely have to declare a mistrial. Although such a mistrial would be a significant setback for prosecutors, they would most certainly seek to schedule a new trial for Holmes as quickly as possible. Sunny Balwani, Holmes’ codefendant, is scheduled for his separate trial after Holmes. 

Follow the Prison Professors blog for regular updates on the Elizabeth Holmes trial and criminal justice topics.

Prison Professors, an Earning Freedom company, works alongside (not in place of) civil and criminal defense counsel to help clients proactively navigate through investigations and prosecutions. Our team also helps clients prepare mitigation and compliance strategies.

If you have any questions or are uncertain about any of the issues discussed in this post, schedule a call with our risk mitigation team to receive additional guidance.

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