Can a judge declare a mistrial or overturn a verdict if a juror was found to use social media websites during a trial, such as Facebook, Twitter, etc.?

While the Sixth Amendment guarantees the right to a fair trial before an impartial and competent jury, courts are reluctant to allow an inquiry into what transpires during jury deliberations. The reasoning is that if jurors knew their deliberations could be examined after the verdict, they might be discouraged from engaging in a full and frank discussion in the jury room or become unwilling to return an unpopular verdict. In addition, the rules of evidence do not allow an inquiry into jurors' emotions, mental processes, or beliefs. An exception occurs when there are allegations that extraneous prejudicial material was improperly brought to the jury's attention, or that outside influences were improperly brought to bear upon a juror. A defendant has a right to have the jury deliberate free from distractions and outside influences. Before the court agrees to conduct an inquiry, it likely will require clear and substantial evidence that a specific impropriety occurred which could have prejudiced the trial. In Florida, where you are from, the courts employ a "harmless error" standard. For example, they have held that the presence of unauthorized publications in the jury room warrants a new trial unless there is no reasonable possibility that jurors were affected by them. The burden to show the unauthorized presence of the publications was harmless is on the State. In some jurisdictions, courts presume prejudice whenever a jury is exposed to extraneous information, while in others prejudice is only presumed if the extraneous information is of a considerably serious nature and the party seeking the new trial bears the burden of demonstrating the likelihood of prejudice. Courts also presume that jurors follow instructions. These days, courts routinely instruct jurors not to consult reference materials, internet websites and blogs, or to communicate with others about the case on their cell phone, Blackberry, through e-mail, text messaging, or on Twitter. Jurors also are told to disregard anything they may have seen or heard outside the courtroom. The Supreme Court has held that due process does not require a new trial every time a juror has been placed in a potentially compromising situation as it is virtually impossible to shield jurors from every contact or influence that might theoretically affect their vote. The decision as to whether allegations of misconduct involving the use of social networking sites or Twitter warrant a hearing rests with the Judge. If there is strong factual support for the claim that a juror improperly consulted outside material or communicated with persons outside the jury during deliberations, and if the nature of the purported communication was prejudicial, a judge may conduct an inquiry, after which he or she may overturn the verdict and grant a new trial.