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FEMALE VOICE: A mistrial declared today in the case of a Butler County ROTC instructor accused of sexually molesting two students--testimony had only been underway for a few minutes when the judge halted proceeding. Channel 4 Action News reporter Bob Mayo explains the decision.

BOB MAYO: Both of the boys who are the alleged victims in this case were prepared to take the stand and testify against their former junior ROTC instructor. But this trial in the Butler County Courthouse ended within minutes of when it began.

Fifty-one-year-old Kevin Johnson is accused of sexually assaulting two of his Seneca Valley High students while he was their junior ROTC instructor. But it was the words of the Jackson police chief from the witness stand that triggered a call from defense attorney David Shrager.

DAVID SHRAGER: The first witness was called by the commonwealth. He made a statement that I felt was not proper for the jury to hear, made a motion for mistrial.

BOB MAYO: The testimony of the police chief that Johnson had declined to take a lie detector test about the allegations against him.

DAVID SHRAGER: There are certain tests that are given that don't have the degree of scientific necessity that a commonwealth can tell a fact finder or jury about them. They're just not that accurate.

BOB MAYO: Assistant Butler County District Attorney Mark Lopes, the prosecutor in this case, tells us, "The DA's Office will not comment on the mistrial itself. But we will retry as soon as possible."

DAVID SHRAGER: Both sides prepared hard and were ready to go to trial today. And now that'll be delayed for some time. Johnson and his attorney are not discussing details of their defense outside the courtroom. He went through a formal arraignment. He entered a plea of not guilty. And he asked for a jury trial.

BOB MAYO: There's no word yet from the Butler County Courts on when the second trial may begin. Bob Mayo, Channel 4 Action News