MOORPARK -- No signs of the remains a 16-year-old boy believed to be buried next to a Ventura County freeway were found Wednesday, even after a bone-sniffing dog let out a series of barks.

The dog, Buster, twice led FBI agents and heavy-equipment operators to focus the search on the eastern wall of a 12-foot-deep pit that has been excavated along the southbound 23 Freeway at the Tierra Rejada Road offramp.

Into their third day of digging, cold case investigators from a half-dozen jurisdictions searched for the remains of Roger Dale Madison, who was last seen just before Christmas 1968.

The dog's barks indicated that he smelled decaying human bones.

"That's how Buster says he's happy, and that he thinks he's found a bone," Los Angeles police Detective Vivian Flores said.

But as the sun set and the excavation stopped, Flores said that no signs of a body had been found. The dig is a follow-up to 1970 confession by Mack Ray Edwards, California's most prolific serial killer of teens and children. Edwards, who worked at freeway construction sites, was never convicted for the murder of Madison, but was sent to death row for killing at least six children in a crime spree dating from 1953-1969.

He committed suicide at San Quentin prison in 1971, but left a confession that Madison had been slain in an orange grove in Sylmar and buried next to a freeway near Thousand Oaks.

Pasadena nonfiction author Weston DeWalt and LAPD Detective Vivian Flores worked on the case

for three years. They found a retired Caltrans engineer who supervised Edwards and knew where the bulldozer operator was working in December 1968.

Sisters and brothers of the teen's deceased parents have given LAPD detectives DNA swabs to be compared with any human remains found in Moorpark.

A hydraulic rock-crushing machine, similar to the ones that demolished earthquake-damaged freeways in 1994, was lent to the project by the Penhall Company of Anaheim and credited by LAPD and Ventura County sheriff's deputies with dramatically increasing the speed of the dig.

Using high-tech sniffer machines that can ferret out minute concentrations of gases emitted by decaying bones long after flesh has left bodies, scientists with the FBI and Oak Ridge National Laboratory are using the recovery effort to perfect the science of cadaver searches.

"The FBI says we are writing the book here on how this type of investigation is done in the modern era," said Ventura County sheriff's Capt. Richard Barrios. "The findings here are setting the bar for the science of discovering clandestinely buried bodies."

One Oak Ridge expert said it was "highly probable" that human remains will be found.

Arpad Vass said in a telephone interview that investigators doing work similar to the "C.S.I." television show will be using lessons learned from Moorpark for years.

Ventura County homicide detectives said any possible remains could be Madison's, or those of another unknown child, as Edwards had made a rambling, sometimes incoherent confession in 1970.

More than 40 agents from the Los Angeles FBI field office are taking turns sifting tons of dirt by hand through large screens set up at the interchange of the 23 Freeway and Tierra Rejada.

Work will resume at the site at 7:30 a.m. Thursday. The project may extend through next Friday, and until then the southbound 23 ramp to Tierra Rejada Road will remain closed, as is the onramp from westbound Tierra Rejada to the southbound 23.