How do we identify human remains?

The case of a surgical implant found inside a Queensland crocodile has highlighted the challenges forensic scientists face when trying to identify human remains without much evidence to go on.

Did the crocodile eat a human with a surgical implant? If so, could the implant — a metal plate and some screws — be used to identify the victim? Or did the implant come from a dog?

Death by crocodile is reasonably rare. In the past decade, there have been about 67 crocodile attacks in Australia, a quarter of which were fatal.

Victim identification can be impossible in these cases, unless a body part with a unique characteristic is recovered, such as a medical device with a serial number. It’s just one of a range of potential techniques to put names and faces to hundreds of unidentified human remains in Australia.

Forensic examination of human remains is crucial to establish the person’s identity, and cause and manner of death. This way they can have a proper burial, families can get answers, death certificates can be issued and justice can be served.

It is essential for identifying missing persons, disaster victims and casualties of war.

The big three: fingerprints, teeth, DNA

When human remains are recovered, three primary scientific methods are traditionally used to identify who they belong to:

  • fingerprint analysis, which looks at the skin patterns on the tips of fingers

  • dental analysis, which looks at the teeth and any dental work, such as crowns and fillings

  • DNA analysis, which looks at DNA profiles recovered from soft or hard body tissues.

This information can then be compared to a database of fingerprint, dental or DNA records.

Implants and x-rays can also be useful

The discovery of medical implants during an autopsy can also be informative.

These include prosthetic joints, breast implants, pacemakers or dental implants. Investigators may be able to link these to patient records via their unique markings, including a trade mark, date of manufacture and serial number.

In Australia, the Australian Orthopaedic Association National Joint Replacement Registry and Australian Breast Device Registry collect and store information that can allow people who have had joint or breast surgery to be identified.

But there are no national registers of heart or dental implants. Such mandatory records would allow implants to be easily traced back to recipients or surgeons.

Forensic scientists can also compare medical images, such as x-rays or CT scans, taken before and after death.

For head images, unique features such as the sinuses or the arrangement and condition of the teeth can be compared.

Body scans can also be used to look for rarer skeletal features, such as fractures, amputations or cancer lesions.

These scientific techniques, either individually or in combination, have been successfully used to identify large numbers of missing persons or disaster victims.

Computerisation, digitisation and miniaturisation of forensic technologies have further improved the identification process. Now, fingerprints, teeth, DNA and medical images can be quickly and easily collected and searched in real time using portable instruments at the scenes of mass disasters.

But there are limits

These methods are only as good as the information we have from when the person was alive. So if someone doesn’t have their fingerprints on file and hasn’t visited a dentist recently, or if close living relatives aren’t available to provide a DNA reference sample or they’ve never had a CT scan, these methods are likely to be useless.

And if a surgical implant doesn’t have unique markings (as in the case of the Queensland crocodile), it makes the task extremely difficult.

So forensic scientists need to explore other methods.

Clues from tattoos and bones