Clues to Jimmy Hoffa's disappearance three decades ago could be buried in the pastures of a Michigan horse farm, but scientists said investigators face plenty of obstacles in finding the remains of the former Teamsters boss.

As the search entered its sixth day Monday, forensic anthropologists who have worked on similar searches and excavations said federal agents have plenty of modern tools at their disposal: ground-penetrating radar, electromagnetic surveying devices and DNA testing if Hoffa's remains are found.

But more than 30 years have passed and the Milford Township farm about 30 miles northwest of Detroit is on dozens of acres of fields and woods, they said.

What's more, skeptics question whether Hoffa's remains are even at the farm: Mayer Morganroth, an attorney for Rolland McMaster, a former Hoffa associate who once owned the farm, said they both believe nothing will be found there.

But officials have said it's a good lead. Investigators have brought in earth-moving equipment, cadaver-sniffing dogs, and anthropologists and archaeologists from Michigan State University.

Scientists stressed that the work is painstaking, requiring the team to strike a balance between properly combing the land without destroying evidence.

"This is going to be more like an archaeological scene than a crime scene," said Jay Siegel, director of the forensic and investigative sciences program at the Indiana University-Purdue University Indianapolis School of Science.

William Bass, professor emeritus of forensic anthropology at the University of Tennessee, said that when he first saw news footage of investigators sticking probes into the land, it told him "whatever evidence they have is not very specific."

The shaftlike probes allow investigators to search for soft spots in the soil that might indicate the outline of a pit, but Bass said more precise information would have prompted authorities to erect sheets to block public view and begin the process of excavation.

A hastily dug grave would leave subsoil above the topsoil and indicate changes in the dirt's color, Bass said.

Most soft tissue would have decayed by now, but scientists said a skeleton or bone fragments could be used to conduct DNA testing to determine the identity. Other clues could still be in a burial pit: any clothing made of synthetics, a leather belt or shoes probably would remain intact, the scientists said. Careful excavation also might uncover footprints at the bottom of the pit, Bass said. In some cases, he has found cigarette butts in a grave — probably from nervous abductors.

"If you have just kidnapped Jimmy Hoffa and you're trying to get rid of him, you're worried," Bass said.

Barring an obvious bullet wound, scientists would have to determine whether any marks or signs of injury on skeletal remains came from the natural course of his life or foul play — a very tricky exercise.

Steven Symes, a professor of forensic anthropology at Mercyhurst College in Erie, Pa., said that after three decades there is less chance of identifying signs of foul play.

But at the same time "the good trauma analysts can actually figure out what happened to that person," he said. "There could be good evidence."