SAN DIEGO, 11:15 p.m. PST March 9, 2001 -- An autopsy on the body of a teenage girl found dying two months ago on a discarded couch in a city park proved inconclusive as to the cause of her death, documents revealed Thursday.

Nia Coleman (pictured, left), 14, had traces of alcohol and a date rape drug in her system, but not enough to be fatal, according to the postmortem tests. The cause of her death is officially listed as "undetermined."

At the time of her death, her blood-alcohol level was 0.02 percent, and she had 6.2 milligrams of gammahydroxy butyrate, or GHB, in her system, said Mike Workman of the San Diego County Medical Examiner's Office.

Dangerously toxic levels of GHB, which rapists increasingly have used to incapacitate women, would be in the hundreds or thousands of milligrams, "so that amount is almost nothing," Workman said.

What's more, the substance sometimes occurs naturally in the body, particularly after death, he said.

According to a pathologist's report, a vaginal injury could have led to an air bubble in Coleman's bloodstream that traveled to her heart, lungs or brain, causing sudden cardiac arrest.

That theory represents the "best mechanism" for explaining the mysterious fatality, according to the document written by deputy medical examiner Christina Stanley.

Still, "in view of the unconfirmed mechanism of death, the manner of death is classified as undetermined," Stanley wrote.

On the night of her death, Coleman had been loitering and drinking with a group of other juveniles and two young men at the northern San Diego park.

At one point, she and 18-year-old Sean Sebastian Smith went off together. Smith ran back a few minutes later, told the group the girl was dead and fled, according to police.

Coleman's friends found her unconscious just before 6:30 p.m. on the foliage-shrouded couch near a trash bin, then called 911. She died at a hospital that night.

Police arrested Smith on suspicion of having illegal sex with a minor, but did not seek charges, pending further investigation.

The case may never result in a criminal prosecution, SDPD homicide Lt. Ray Sigwalt said Friday.

When asked if the girl's death could have been a freak accident, Sigwalt replied: "Your guess is as good as mine."

Previous Stories:

• January 28, 2001: Tests Say Teen Had Little Alcohol Before Her Death
• January 26, 2001: Suspect Arrested In Mira Mesa Teen Death