Transcript for Grand Juror Says He Believe He Knows Who Killed JonBenet: Part 4
Te "20/20" continues. Reporter: Little girl, big mystery. Even after nearly two years of investigation, the murder of jonbenet Ramsey remained unsolved. It was looking like the killer might never get caught. Until, in late 1998, the wheels of Boulder justice jumped into overdrive. The D.A. Presented the case to a grand jury of eight women and four men. Police have been pushing for this day for months. We're at a grand jury stage where the key element is surprise. Reporter: No one is talking about what's going on in the courtroom. And we don't expect a lot of information to come out. Reporter: Grand jury proceedings in Colorado and elsewhere are secret. The penalties for revealing testimony or evidence can be severe, even jail time. In spite of that threat, nearly two decades later, one member of that jury has agreed to talk to "20/20." Given the possible repercussions, we agreed to alter his voice and put his face in shadow. Before you were a grand juror, what did you know about the jonbenet Ramsey case? I saw that there was a little girl dressed up with, in my opinion, a sexual persona, and it disgusted me and I turned off the TV. Reporter: Over the course of more than a year, he and the other grand jurors grappled with the evidence and testimony from dozens of witnesses. The whole jury even took a field trip to the Ramsey home on 15th street. In the basement where she was found, it was actually kind of an obscure layout. And you had to -- to go into -- you come down the stairwell and you had to go into another room to find a door that was closed. It was a very eerie feeling. It was like, "Somebody had been killed here." Reporter: A grand jury does not decide guilt or innocence, only whether there is probable cause to charge someone with a crime. Probable cause means there's enough for us to move forward. The difference between getting an indictment versus proof beyond a reasonable doubt is a huge difference. Reporter: Was there enough evidence to indict John and Patsy Ramsey of a crime? Based upon the evidence, I believe that's correct. Reporter: But if the case went to trial, did he believe that the Ramseys would be convicted? No. Reporter: No doubt? There is no way that I would have been able to say, "Beyond a reasonable doubt, this is the person." Reporter: There was no smoking gun. Not to the point of knowing exactly what happened, or exactly who was involved, no. And if you are the district attorney, if you know that going in, it's a waste of taxpayer dollars to do it. Reporter: Still, the grand jury handed up an indictment accusing John and Patsy Ramsey of not murder, but child abuse, finding they allowed jonbenet to be "Placed in a situation which resulted in death." At least nine of those jurors felt there was probable cause to believe that that crime occurred. And saying that, they were also saying, "I can't tell who did what." I'm not ready to say there's probable cause to believe that either John Ramsey or Patsy Ramsey intentionally and deliberately murdered their child. Reporter: After a year and a half of investigation, the stakes could not have been higher for the district attorney, or the Ramseys. We were prepared to drive to the sheriff's office, turn ourselves in, and be jailed. We had signed a custodial agreement that would put Burke in the custody of my brother. We had to prepare in the event the worst happened. That is a daunting thought. I mean, when you're packing your suitcase, saying, well, what does one take when one might end up in jail? Reporter: But in an astonishing turn of events, the prosecutor nullified the findings of his own grand jury. The criminal justice equivalent of, oh, never mind. I must report to you that I and my prosecution task force believe we do not have sufficient evidence to warrant the filing of charges against anyone who has been investigated at this time. What made this case so unusual is that the grand jury did hand up an indightment on certain charges and the district attorney decided not to prosecute. And I remember John saying, "Now, maybe they'll go after the real killer." Do you know how much evidence it takes to come up with an indictment? About this much. They found nothing in 13 months. There was nothing that pointed to John or to me. Reporter: Then-governor bill Owens was furious. If I could speak to John and Patsy Ramsey, I'd tell them to quit hiding behind their attorneys, quit hiding behind their pr firm, come back to Colorado, work with us to find the killers in this case, no matter where that trail may lead. What do you say to the governor? I would say to governor Owens, you spent three years investigating my family. What are you going to do to find the killer of my daughter? Reporter: A mystery for some. Less so for our mysterious juror. Based on the evidence you were presented, do you feel you know who killed jonbenet Ramsey? I highly suspect I do. Reporter: And who do you think that is? I wish not to answer that question. Reporter: Now the investigation is about to leap ahead, detectives examining 20-year-old evidence under the microscope of the latest technology. Could it reveal a whole new theory of the jonbenet Ramsey murder case?
This transcript has been automatically generated and may not be 100% accurate.