By BBC News Online's Peter Gould in New York

Many relatives of World Trade Center victims will never have a body to bury, but are still desperate to find the remains of their loved ones. Their best hope may lie in the latest DNA analysis techniques.

The families of many of the victims at the World Trade Center still don't know if they will ever have a body to bury.

Three months on, the reality they have to face is that some of their loved ones may never be found and identified.

The need to do everything possible to recover the human remains is felt acutely by everyone working amid the debris.

The firefighters who lost 343 friends and colleagues on September 11 say they want as many families as possible to be able to hold a proper funeral service.

Identifying the dead

Recovering the remains is a grim task, and only the first stage in what is likely to be a very long process, trying to identify those still listed as missing.

We will go on testing until they stop bringing in remains

Ellen Borakove, chief medical examiner's spokesperson

Traditional methods such as the use dental records are still used. Teeth are the strongest material in the human body, and often survive when nothing else does. But many bodies are not intact, and the best hope of identifying them is by extracting DNA from the remains.

In recent years, DNA "fingerprinting" has revolutionised the investigation of crime, often proving a link between perpetrator and victim.

But the technique is increasingly used to help identify the dead after disasters such as plane crashes where there has been a large loss of life.

Largest DNA test ever

The operation to identify those killed in the Twin Towers is the largest piece of DNA detective work ever undertaken. Even with the assistance of laboratories across the United States, it is likely to take at least a year.

More than 10,000 body parts have now been recovered, and all these remains will be subjected to DNA analysis.

So far, laboratory workers have identified the profiles of about 800 individuals, still well short of the 3,000 people thought to have died.

Sifting through the debris is a mammoth task

The fact that more human remains are being recovered every day will bring some hope to grieving families, waiting for news. But some will be disappointed.

"When the planes hit the upper storeys of the towers, there were explosions and bodies were fragmented," says Ellen Borakove, at the office of the chief medical examiner.

"Some of the victims were vaporised or rendered into dust. But we will go on testing until they stop bringing in remains."

Samples of DNA

The families of those still officially listed as missing are being asked to provide items that can be used to provide a sample of the victim's DNA.

Saliva offer the best results, which means gathering up toothbrushes, drinking glasses, cigarette ends and chewing gum. But hairbrushes, electric razors and items of clothing can also provide material.

In addition, samples of DNA from close relatives can also be used to confirm the identity of a victim.

The one worry is how well DNA has survived. Forensic scientists know that time is their enemy, along with the extreme physical conditions at Ground Zero.

They also know that many families are depending on them to help recover the bodies of their loved ones.

Huge operation

As the identification process continues, so does the operation to remove 1.2 million tons of debris from Ground Zero.

The World Trade Center contained 200,000 tons of steel, 425,000 cubic yards of concrete, and 14 acres of window glass.

You don't want to give people false hope, but you don't want to give them no hope

Ellen Borakove

Tons of ash and dust add to the difficulty of sifting through the wreckage for human remains and personal belongings.

Even when the surface debris has been removed, salvage teams will have to remove huge steel beams now buried deep in what used to be the foundations of the towers.

The debris is being taken to sites outside Manhattan where it can be examined properly for evidence. This is not just an operation to recover the dead, it is also a criminal investigation.

Those who counsel the families of New York's victims talk about the need to give them closure. Others prefer to talk of healing.

However it is described, the recovery of the body is an important part of the process.

For some families, that comfort may be a long time coming, if it comes at all.

"I have spoken to many of the families and tried to give them a realistic assessment," says Ellen Borakove.

"You don't want to give people false hope, but you don't want to give them no hope."