IN MAY 1993, a work crew was clearing land for a new fence at a Halliburton research facility, just south of Alvarado, Texas, when one of the men noticed something out of place.
In a brushy, wooded area just off a service road for Interstate 35W, he saw what appeared to be a human skull, and next to it, some other bones, a faded blouse and jewelry. The remains had been there so long, a brierwood bush was growing through the blouse.

The Johnson County medical examiner's office did what it could, determining that the remains belonged to a young woman, between 16 and 27 years old, anywhere from 5 feet 4 to 5 feet 9 inches tall.

"We theorized she'd been out there about 10 years," said Sgt. David Cole, lead homicide investigator for the Johnson County Sheriff's Office.

There were no further clues to the woman's identity, and Johnson County had no missing-person reports that matched the bones.

The skeleton was kept at the medical examiner's office until a visiting fire inspector declared the bones a bio-hazard, and ordered them destroyed.

Instead, one of the nurses hid them in a box and stuck it under a cabinet in a storage area.

"She just said, 'We're not getting rid of these,' and she kept every bone we had recovered," Cole said.

Thanks to one stubborn nurse - plus dedicated investigators and the relentless growth of technology - those bones eventually gave up their identity - but it took another 10 years.

In mid-2004, DNA research and a fledgling national database of DNA profiles made it possible to link the Alvarado bones to a 19-year-old Texas woman who had disappeared in 1982, more than a decade before her skeleton was discovered.

Authorities believe the same technology could help Philadelphia and other jurisdictions deal with some of their longest-running mysteries - thousands of unidentified human remains and tens of thousands of missing-person cases that have kept families in limbo for years.

Two recent cases have focused attention on Philadelphia's problems in this area. Two badly decomposed bodies lay unidentified in the city morgue for months - in one case, more than two years - at the same time that the respective families had filed missing-person reports with the Philadelphia Police Department and had tried to publicize their searches.

National authorities say there are similar problems throughout the country. To deal with them, support is developing for a strong national reporting system for missing persons, coupled with a national database of DNA profiles, covering unidentified remains, missing persons and their relatives.

"What's going on in Philadelphia is not an isolated situation," says Bill Hagmaier, a 24-year FBI veteran who heads the International Homicide Investigators Association, a Virginia-based group of police officers and prosecutors who deal with murder cases. "This is a silent crisis for the whole nation. . . . We have about 40,000 unidentified dead in the United States, and they are not getting the attention they deserve. "

The Bush administration has committed $1 billion over five years to upgrade DNA testing at laboratories around the country and to promote its use throughout the criminal-justice system.

One component of "The President's DNA Initiative," announced in March 2003, is to "ensure that DNA forensic technology is used to its full potential to solve missing-persons cases and identify human remains. "

A national DNA database, initially created by the FBI in 1998 to handle DNA samples from convicted criminals and crime scenes, has been expanded to include DNA profiles from unidentified remains, missing persons and relatives of missing persons.

So far, the expansion into missing-person cases has been slow.

The FBI has collected DNA profiles from 2.7 million convicted offenders and from 125,000 crime scenes, but as of this week the database includes DNA data from only 244 missing persons, 319 unidentified remains and 719 relatives of missing persons.

"The missing-persons part of the database is really in its infancy," said Dr. Tom Callaghan, the molecular biologist who is official "custodian" of the FBI's National DNA Index System.

So far, very little of the missing-persons data has come out of Pennsylvania.