"Typically if a case goes beyond a week, it usually bodes well for the defendants," Dr. Marshall Hennington, a trial and jury consultant for Hennington & Associates, tells PEOPLE. Hennington, who has followed the trial closely, identifies a number of issues that could be responsible for the impasse. "It could be that there's a clash of personalities and no one's willing to compromise in order to have a unanimous decision," he says, adding that the Etan Patz trial is an especially difficult case because so much time has passed since the crime. "This crime took place years and years ago," Hennington says. "With the amount of time that's gone by, the evidence is just not there. First off, there's no direct evidence linking Hernandez to this crime. Second thing is, there were no eyewitnesses to this crime. Third thing is there's no DNA. They just have a videotaped statement to police. That's all prosecutors have." And Hernandez's own word is not enough to legally convict him. The lack of direct evidence tying Hernandez to the crime is particularly problematic. "These jurors may feel they don't necessarily see this person committing the crime because they don't perceive this person as being the violent character he's being portrayed to be," Hennington says. "He did not have a history of killing other people. He's not a serial killer. That makes it difficult." Defense attorney Harvey Fishbein told jurors back in January that Hernandez, now 54, is mentally ill and that his so-called confession was actually a product of his mind, the fantasy of someone who's deeply disturbed, but a fantasy nonetheless. And with no other evidence, prosecutors can't prove otherwise. "If prosecutors had a clear and convincing case that this man killed that child, this would have been over with at this point," Hennington says. And each time Justice Maxwell Wiley sends the jury back to deliberate, the risk of a mistrial grows. "Twice these jurors have declared that they're deadlocked," says Hennington. "Mr. Fishbein has been arguing that this amounts to coercion and that the jury is obviously hung and that the judge should declare a mistrial, but he hasn't." In such a high-profile case, it's understandable that the judge wants the jury to come to a decision. But "if they go back again [a third time], there's going to be some real legal issues regarding the judge's performance," says Hennington. He adds that Justice Wiley is really only delaying the inevitable: The jury is unlikely to come to a decision no matter how many times he sends them back. "You're talking two weeks already," Hennington says. "We haven't had jurors deliberating in any of the trials I've been involved in for more than two weeks over the course of my 17-year career."