A special four-part series:

Part I   Part II  Part III  Part IV

Four-and-a-half years after the murder of JonBenet Ramsey, no one has been charged with her death and key questions remain unanswered.

Were the marks on JonBenet's back made by a violent intruder who tortured the child with a stun gun? Was her death really a homicide, or an accident subsequently staged to look like a homicide?

Former detective Lou Smit is the only person actively looking for the truth. Working out of his home, Smit has dedicated his retirement to finding the six-year-old beauty queen's killer.

Smit retired from the JonBenet investigation because he thought investigators were wrong in suspecting the little girl's parents.

"I would like to see that the Ramseys, instead of having an exclamation point after their name, that at least there's a question mark," he said.

Smit thinks a pedophile broke into the Ramsey house through a basement window, where he waited for the family to return from a Christmas party before taking JonBenet from her bed.

"She was taken downstairs into the basement, into probably the furthest corner of a very cluttered, dirty basement," he said.

Smit's convinced that two red dots found on the JonBenet's lower back prove a stun gun was used in the fatal attack.

"If a stun gun is used on JonBenet, it's very likely it's not the parents," he said.

Once in the basement, Smit says, the intruder choked the child with a garrote before hitting her on the head to make sure she was dead.

"This [garrote] was constructed for control. If Patsy Ramsey would strangle to make it look like somebody had strangled her daughter, why not do it with your hands? Do it with just a rope ... why build a handle?" he argued.

But Boulder police have a different theory. They believe the 8-and-a-half inch fracture found on JonBenet's skull was caused by accident, and that her strangulation followed to fool investigators into forming an intruder theory.

Autopsy consultor Tom Henry substantiates this hypothesis. He believes JonBenet may have survived unconscious for 15 minutes after an initial blow to the head before being strangled.

"The fact that she's got this extensive injury described as a blood clot in the scalp indicates a little longer period of time that she had to survive ... a little more blood pumping under pressure for a longer period of time," he said.

But Arapahoe County coroner Michael Doberson doesn't see it that way. He never saw the body, but worked from autopsy photos and experiments with anesthetized pigs.

"Everything is consistent with a stun gun," said Doberson.

Forensic scientist Henry Lee, a lead consultant on the Ramsey investigation, shrugs off both conclusions. He says the only coroner to believe is the one who actually examined the body.

John Meyer performed JonBenet's autopsy, and reported that the marks on her back were abrasions, not electrical burns caused by a stun gun.

"The best person to make this interpretation is the medical examiner who saw the body. We only see pictures," said Lee.

Will the person responsible for the murder of JonBenet Ramsey ever be exposed? One attorney thinks the suit he's filing in civil court may bring an end to this nearly five-year-old mystery ...