Doctors are gearing up for the largest effort in the annals of forensic medicine: identifying the dead in the World Trade Center attacks.
The scientists always knew the identifications would be an arduous task, but with more than 6,000 people still unaccounted for and relatively few bodies recovered, it is turning out to be a far bigger job than they expected.
The effort has a dual purpose -- to provide evidence for those investigating the attacks and to bring answers to families and friends whose lives may be suspended in unresolved grief until there is evidence of their loved one's fate.
Some identifications have already come from such time-honored techniques as autopsies and studies of dental records, X-rays or fingerprints. Some people have been identified by scars, rings or other pieces of jewelry.Continue reading the main story
But the destructive force unleashed in the collapse of the World Trade Center was so great that many bodies are beyond detection by these methods. So doctors are turning to sophisticated techniques to compare the DNA of unidentified bodies or body parts with that obtainable from combs, toothbrushes or other personal effects of the missing.
If these objects do not yield usable cells for comparison purposes, the doctors will turn to close relatives of the missing, hoping a comparison of their DNA will help identify the dead.
Forensic use of DNA testing began in 1985 and has evolved into what law enforcement experts call the most powerful tool since the development of fingerprinting in the late 19th century. In the mid-1990's DNA testing was used to identify exhumed bones as those of Czar Nicholas II and members of his family who were executed in Russia in 1918. In 1998, DNA testing identified the ''unknown soldier'' killed in Vietnam.
Now DNA testing has become standard in mass disasters. Improved techniques provide speedier testing and greater precision, allowing doctors to make identifications that would otherwise be impossible. The average person has 100 trillion cells; in theory, identification is possible from just one.
The New York City medical examiner's office has pledged to test DNA on all tissue it receives from the World Trade Center disaster site, although forensic specialists say some victims may never be identified.
Dr. Robert Shaler, who directs forensic biology for the medical examiner's office, estimated the day after the attacks that his laboratory may have to perform 20,000 DNA tests on the remains. Now he knows there will be far more tests.
''Things have been changing almost hourly since then,'' he said, and some experts now predict that as many as a million DNA tests may be required. He said the city would do whatever is necessary to identify as many victims as possible.
''We have two public missions -- one to New York City and the victims, the other to the city's criminal justice system,'' Dr. Shaler said in an interview.
Dr. Shaler says his is the largest forensic DNA facility in the country; still, it cannot handle the expected volume of tests. So his team has welcomed the aid of the New York State Police and contracted with a number of private laboratories to do them.
Presumptive identifications of some victims may be made from pictures of the deceased and through wallets found on their bodies. Tattoos can be useful, but not always. Sometimes family members are unaware that a relative had a tattoo.
Identification carried in a wallet can be useful, but only if officials know it belonged to the person on whom it was found -- which is not always the case. ''How do we know he wasn't a pickpocket?'' asked Dr. Charles Wetli, the Suffolk County medical examiner.
Even in-person identification of bodies by relatives may not be reliable. Dr. Wetli recalls a case from his work in Miami in which a bereaved man identified a body as that of his wife -- even though the body, a man's, had been shown to him by mistake.
In 1996, Dr. Wetli led the forensic investigation of the victims of the crash of TWA Flight 800 off Long Island. When terrorism was initially suspected, his team decided it could not rely on presumptive identifications and used DNA testing, Dr. Wetli said. DNA testing had been used in identifying more than 80 Branch Davidians who died during a standoff with F.B.I. agents in Waco, Tex., in 1993. DNA was also used to identify all but 2 of the 141 Ukrainians and Russians aboard a Russian airplane that crashed near Spitsbergen, Norway, in 1996.
Dr. Jack Ballantyne, who ran the DNA laboratory in Dr. Wetli's office, said the Suffolk County team used DNA to identify 22 of the 230 victims in the TWA crash who would not otherwise have been identified. It was the first time such testing had been used in a commercial airplane crash in the United States.
DNA testing also led to the identification of all bodies in the crash of a Swissair plane in 1998 and an Egypt Air plane in 1999, said Dr. Michael M. Baden, the chief forensic pathologist for the New York State Police.
DNA identification of the victims and hijackers could be important in a criminal investigation by aiding law enforcement officials in bringing any accomplices to trial.
But the World Trade Center disaster is many times larger than the TWA, Swissair and EgyptAir crashes. Although the forensic specialists have passenger lists for the two hijacked planes that crashed into the World Trade Center, there is no way to list everyone who might have been in the Trade Center buildings and surrounding area during the attacks and subsequent collapse of the towers.
The process of recovering bodies and tissue from the site is agonizingly slow and grisly. As workers sift through the rubble, they are finding more body parts than bodies. Because no pathologist can tell which piece of tissue came from which victim without DNA testing, forensic scientists may test scores of tissues that turn out to be from the same person.
As of yesterday morning, 152 bodies had been identified and their relatives notified, the medical examiner's office said, and all identifications have been through traditional means like fingerprints and dental records. Dr. Shaler said his laboratory had extracted DNA from 3,200 of the 3,600 tissues it has received and has produced DNA profiles of 839 among them. He added that this week he expected to send the extracted DNA to the private laboratories, where scientists will try to match them with DNA submitted by relatives or from personal items.
In the World Trade Center disaster, exploding jet fuel and crumbling buildings may have charred and pulverized many bodies before and after they fell.
Some bodies, even bodies that fell from very high floors, were still intact after hitting the ground. But most of the remains found at the site showed signs of injury severe enough to make visual identification impossible. Some were severely burned.
So workers at the site are struggling to recover them as quickly as they can, under dangerous working conditions. Microbes, enzymes, insects and other environmental factors accelerate decomposition and degrade DNA, usually within a few weeks. The problem ends once tissues are received in the laboratory, where the remains can be refrigerated for long periods until ready for DNA testing.
Because the rate of decomposition depends on heat, light and humidity, the effect of these environmental factors will depend on the location of the bodies and tissue in the rubble. Even so, forensic workers can often obtain usable tissue by cutting into deep muscle.
Dr. Shaler's lab is using automated systems to extract DNA from up to 4,000 tissue samples a day. The material will then be sent for testing at two private labs -- Myriad Genetic Laboratories of Salt Lake City and Celera in Rockville, Md., one of the laboratories that led the effort to sequence the human genome.
Meanwhile, toothbrushes, combs, locks of hair and other personal effects are being sent for DNA extraction at the New York State Police Laboratory in Albany. Swabs taken from the mouths of relatives have also been sent there for DNA extraction.
The State Police will also send the DNA for testing at Myriad and Celera. Dr. Shaler's laboratory, the state police laboratory and another yet to be chosen will also test 5 percent of all samples as a quality control for the tests performed at the private labs.
All the teams are receiving software from the Federal Bureau of Investigation to help match DNA from victims' tissues with their personal items. The teams are also developing a computer network for more efficient communication.
Two types of DNA testing are available, and the choice will depend largely on the state of the tissue.
In both types, the findings from tests on the remains are compared with those from the samples obtained from close relatives or the victims' personal effects, said Dr. Jack Ballantyne, who did the DNA testing in the TWA crash and who is now a professor of chemistry at the University of Central Florida in Orlando and assistant director of its National Center of Forensic Science.
If needed, the scientists can also seek lipstick or lip balm, underwear, swabs used in a recent Pap test or organs or other tissue that pathologists have stored after removal in surgery.
In tests of preserved tissue, the forensic experts can directly match the DNA extracted from the nucleus of cells from the victim with DNA recovered from personal effects like a toothbrush. Also, the victim's DNA can be compared with that of close relatives.
A standard nuclear technique is S.T.R. (for short tandem repeats), which identifies the sequence of the four chemicals, or nucleotides, that form DNA.
The S.T.R. technique focuses on 13 particular sites, or loci, spread out over the 23 pairs of chromosomes that are standard in the F.B.I.'s national database. The DNA from the 13 sites is in nonfunctional areas of the genome. On each of the 13 loci the strings of DNA repeat themselves and the number of repetitions tends to vary among people. So the number of repeats at all 13 yield a probability that a match among unrelated individuals is less than one in a trillion.
When tissue has decomposed, the scientists use mitochondria, organelles inside the cell, separate from its nucleus, that have their own DNA. Mitochondrial DNA can survive in hair, teeth and bones.
Because mitochondrial DNA is inherited only from the mother, samples used for comparison with a victim's must come from either a maternal relative or the victim's personal effects.
So if the missing victim is female, samples obtained from her mother, maternal grandmother, siblings or children can provide useful comparisons.
But comparative samples from a male victim can come only from his mother, maternal grandmother, maternal aunt or uncle or any sibling, but not from his children.
If two or more victims are descended in the female line from the same woman, their tissues cannot be individually identified from mitochondrial DNA. But they could be distinguished by nuclear DNA tests.
The caveats take on critical significance in the World Trade Center attacks because all the hijackers were male and obtaining samples from sisters or mothers seems unlikely.
Even so, identification of hijackers could be made from personal effects that law enforcement officials collect from the hijackers' homes in this country, or even in their native countries. Such effects could include fingerprint residues and dried saliva left on a coffee mug or envelope.Continue reading the main story