Bones: animal or human?

Categories: Forensic Casework experiences, Sciblogs

Although this isn’t really my area, some of my colleagues work with interesting ‘things’ that are found at crime scenes or what turn out to be crime scenes, namely bones.

A huge amount of police time can be taken up in tackling the problems of ‘stray’ bones found by members of the public or unearthed during building works.  The first question is usually, ‘are they animal or human?’  While this is being resolved, the scene needs to be made secure, someone deployed to sort it out and all the paperwork completed.  The best (and fastest) way forward is to photograph any bones with a scale and email the image to someone who knows: a forensic anthropologist such as Professor Sue Black and the team at where they provide a 7-day service with a rapid turnaround time – and an answer!  To-date, the fact that some 90% of the images they have received have been animal shows how much police time has already been saved.   Perhaps our very own Dirt Digger can help with New Zealand finds?!

For best results, all photos should be taken on a clear background with a legible scale. These photos show examples of:

what not to do….

what should be done….

One of the most frustrating problems that can arise is the casual discovery of bone, often handed in by dog walkers, gardeners or building contractors. Once the bone is identified as human the question is ‘how old is it?’ Human remains can often be seen to occupy specific places in the ground or on building sites and an archaeologist can usually give a reasonable answer as to whether the remains are of ‘forensic interest’.

However, when there is no obvious buried or concealed context the problem becomes much harder.  Sometimes, bones can be traced back to a source such as a scavenged burial and the archaeologist can be brought in again but, if not, what’s the next step?  Visual examination of whether or not the bone(s) ‘look’ old or not is unreliable and usually inaccurate and most of the scientific techniques available are unlikely to be very helpful in establishing forensic relevance.

Radiocarbon dating is one of the better ways forward, not because it can necessarily produce a precise date, but because it can sometimes determine whether the body predates or postdates the 1950s.  The reason for this is the so-called ‘bomb effect’, caused by the atomic bomb detonations, which significantly affected atmospheric radiation at that time and can be detected in organic material that incorporated the radioactive material.  Because this peak of radiation tailed off, it may be possible to calculate where on the ‘tail’ the sample sits, thus helping to give it a more accurate date (allowing, of course, for analytical error, sample type, etc.).

Radiocarbon dating is a complex process and there is a limited number of laboratories offering this service; New Zealand is, of course, the proud owner of a cutting-edge instrument.

If the bones prove to be within forensic timescales there may be dermestids present (a type of skin beetle most commonly encountered by humans as pests in stored products and carpets, although several species will also consume decaying carrion). They are therefore found with regularity by the forensic entomologist (such as Dr John Manlove at MFL in Oxford) in larger numbers where bodies have been decaying for longer as they have a distinct preference for drier feeding material.  Dermestids will feed on the fibrous tissue which remains after the bulk of the biomass of a carcass has been consumed by other insects.  They will clean all of the tissue from bones leaving only the skeleton remaining.

Dermestids can be introduced artificially in the laboratory to clean soft tissue from bones.  This has the advantage of resolving fine damage in situations where a more aggressive technique may cause damage to the bone itself. The process is a natural one which, for example, will clean the tissue from human vertebrae within a few days.  MFL has one of the two breeding colonies of dermestids in the UK (now that would be one of those “more interesting work stories” and it definitely sounds like something you’d see on Bones…).

All in all, discovery of a single bone can lead down roads to all sorts of interesting endings….

[written with great assistance from Dr John Manlove]

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Dr Anna Sandiford

The Forensic Group was established in 2008 by Dr Anna Sandiford, a Senior Forensic Science Consultant with many years’ experience in New Zealand and overseas who started her forensic science career in 1998.