ON AUG. 12, 2004, a police marine unit pulled a woman's body from the Schuylkill, near 61st and Passyunk, not far from the South Philadelphia refinery complex.
She apparently had drowned. Investigators at the city Medical Examiner's Office found no evidence of foul play or unusual injuries.

She was about 5-feet-5, 133 pounds, maybe 30 years old, authorities estimated, but that was mostly a guess.

Her body was partially decomposed from its time in the river, which is especially damaging to tissue in the warm summer weather. Her race was uncertain - maybe mixed. No one could say for sure how long she'd been in the water.

But there were other clues to her identity.

Beneath the men's thermal underwear she was wearing, there were tattoos: the letters HAL on her abdomen, and a Chinese character of some sort on her right calf.

She wore white high-top sneakers, Converse, with pink laces, and around her neck was a red and blue lanyard with a keychain, initialed "PCOM," and four keys.

Close to 3,000 bodies a year come into the Medical Examiner's Office on University Avenue in West Philadelphia. The office sits on the edge of the huge health-care complex that includes the Hospital of the University of Pennsylvania and Children's Hospital.

For each body, the M.E.'s office is supposed to identify the deceased and establish the cause of death.

More than 90 percent of the time, it's routine. The bodies come in during the day, are examined first thing the next morning by doctors, and identified by relatives. The bodies are sent to funeral homes within 48 hours, for burial or cremation.

But perhaps 300 times a year, a body arrives and nobody steps forward immediately to identify it.

Those cases go to David Quain, chief investigator for the Medical Examiner's Office, and his eight-member staff.

Quain, 42, was the official who was reading the Daily News three weeks ago and noticed a brief reference to a North Philadelphia woman, Unisha "Niecey" Jefferson, who had disappeared in April 2003, at age 38, last seen near 22nd and Lehigh.

Something clicked. In September 2003, the police had found a woman's decomposed body in an abandoned factory building on Marjie Street, about four blocks away. Quain had never been able to identify the corpse.

Over the following weekend, the M.E.'s office contacted Jefferson's family and obtained an old X-ray of her head and lower jaw.

It was a positive match - ending a 2 1/2-year ordeal for Jefferson's family and closing one of Quain's oldest open cases.

Prompted by the Jefferson case, City Council voted last week to hold hearings on how the city tries to match unidentified bodies with missing-person reports.

The numbers fluctuate, but on any given day, Quain's unit may be struggling with 10 to 20 corpses for which it has no names.

Currently, the number is 12 - unidentified remains from 12 bodies discovered in Philadelphia over the past four years.

The list includes eight men and four women. They're equally divided, roughly, between whites and minorities, though it's sometimes difficult to tell.

Four of the 12 have already been cremated, after a dentist removed their lower jaws for future reference, in case dental records or DNA samples become available to attempt a match.