The arm found outside a Woodbridge restaurant last weekend has provided some interesting and challenging police work, Prince William County officials say, but they predict they will never determine its origin.

Authorities believe the arm was stolen from a laboratory or medical school because it was removed from a human torso in textbook surgical fashion. Also the fact that the arm was skinless, bloodless and smelling of formaldehyde, suggests that it came from a medical school laboratory, police said.

"Anybody who has access to an anatomy class could have access to these parts," said Dave Watson, the investigator assigned to the case.

Since the arm was discovered, palm forward against the door of the Featherstone Square McDonald's early Saturday, Watson has been calling area medical schools asking, "Are you missing an arm?" By late this week the calls had yielded no results.

If police can find out where the arm came from, they might be able to link a person to its theft. The arm, which has been cremated, yielded some fingerprints, hairs, fibers and other evidence, police said.

It is likely that the arm did come from a medical school, said Dr. Martin Dym, chairman of Georgetown University's department of anatomy and cell biology. Such a case is rare because of the controls most medical schools try to put on cadavers. Officials from medical schools at Georgetown and the University of Virginia said the bodies are kept in locked storage, with the combinations changed every so often.

"We take the protection of cadavers very seriously," said Carla Harrington, assistant director of the medical center news office at U-Va.

Dym, who checked his cadavers for a missing limb and found all accounted for, said that if a student were caught removing human remains from university grounds, the person would face expulsion.

"In the lab we don't allow joking," Dym said. "Students are taught to respect those bodies as though they are alive."

In Virginia, medical schools receive bodies from the state medical examiner's office in Richmond. The office collects about 500 bodies a year, primarily from people who will their bodies to science.

Medical schools typically pay the examiner's office about $400 for each processed body. Other schools such as Georgetown receive bodies through individual donations.

Watson is not quite sure what he would charge the culprit with, but he is sure of one thing:

"I wouldn't like it if a part of one of my relatives was found alongside a fast food restaurant," Watson said. "The people who donate their bodies to medical science deserve better than that."