Hungry Burglars Beware! Fingerprints Can Be Developed On Food

A number of burglars are unable to resist the temptation to snack on a piece of fruit or chocolate whilst relieving the householders of their more valuable worldly goods. 

 

But rather than taking their apple cores home or eating a whole chocolate bar, many burglars will discard the remains of their snack at the scene  - and leave behind valuable forensic evidence in the form of teeth marks.
 

In Adelaide, a burglary took place in an up-market chocolate factory.  The burglar sampled a few of the products but left the half-eaten bars at the scene.  A forensic odontologist was able to match the teeth marks in the partially-eaten chocolate bars with dental impressions taken from a suspect. 

A quick online search will find many other, similar, examples.

 

In general, food is overlooked as a source of forensic evidence.  However, a perpetrator may handle a piece of food at a crime scene, even if he/she does not eat it.  Consequently, the potential exists for an apple or an orange, for example, to yield fingerprint evidence. 

An item of food may have a porous or non-porous surface, which may be smooth or rough, but it is unlikely to be completely uniform across its surface.  This makes it difficult to choose the best technique for developing fingerprints.

Some techniques are designed specifically to recover fingerprints from porous surfaces, whereas others are designed for non-porous surfaces.  Using the wrong technique may damage the fingerprint and the evidence will be lost.

Until recently, fingerprints had only been recovered from food by scientists from Slovenia and India.  Scientists in the UK were, naturally, interested in these results.  However, the chemicals that were used in the Indian and Slovenian studies are not used to recover fingerprints in the UK.

Scientists at Abertay University in Scotland set out to discover whether they, too, could recover fingerprint evidence from food, but without using the chemicals in the Indian and Slovenian studies.

They started out using conventional UK chemical techniques, but, as expected, the results were disappointing. 

They then turned to Powder Suspension, a thick, tar-like substance that is used to recover fingerprints from the sticky side of adhesive tape.

Here is a video showing how fingerprints can be developed on the sticky sides of duct tape, masking tape and electrical tape.

By modifying the consistency of Powder Suspension and making it more dilute, the Abertay researchers obtained identifiable prints on smooth-skinned fruit and vegetables, including bananas, apples and onions. 

The technique was less successful on potatoes, which are rough-skinned, and eggs, which are porous.

Much more research will need to be carried out before this technique can be used operationally on food at crime scenes.  But, it should give potential burglars something to ponder.  Food for thought, you might say............

Do leave a link to your book/story in the Comments section.  I'd love to read your work.



 

Super-speedy DNA extraction technique is perfect for crime drama

In a single episode of CSI, the featured crimes are solved to everybody's satisfaction and all loose ends are nearly tied.  Those of us with forensic knowledge will probably think 'Yeah, right', but are willing to suspend our disbelief.  It is entertainment, after all.

 

Now, however, solving a crime in an hour may not be so far-fetched after all.

 

 

 

Image courtesy of www.all-about-forensic-science.com

 

 



Engineers at the University of Washington, in collaboration with a company called NanoFacture, have created a device that can extract DNA from body fluids in a matter of minutes.

 

DNA extraction is a complex process, which can take 20 - 30 minutes to complete.  It also requires toxic chemicals, so it is not environmentally friendly.

 

This new extraction technique uses microscopic probes.  First of all, the probes are dipped in the body fluid.  Then an electric field is applied within the fluid.  This causes the DNA molecules to stick to the probes. 

The DNA molecules therefore become trapped on the probe surface.

 

This whole process from body fluid to pure DNA takes only 2-3 minutes.

 

Once the DNA has been extracted, a profile can be generated in the usual way.

 

Here is a link to an article which describes the technique in more detail.

 

New Device Can Extract DNA In Minutes

 

Although the article is slanted more towards medical application of the technique, its potential value in forensic investigations is acknowledged.

 

Here is a (very) short video showing the equipment in use.

 

 

Given that many forensic laboratories have huge DNA analysis backlogs, the time savings on the extraction process could make a considerable difference to throughput.

 

From a crime writer's point of view, this technique offers another way to inject realism into your plotting, but without the need to compromise on reality (unless you want to, of course). 

 

Which forensics techniques do you use in your writing?  Why not let me know in the comments section below; don't forget to include a link to your book or story.

Using Forensic Entomology to establish Post-Mortem Interval

Forensic entomology is 'the use of insects and their arthropod relatives to aid legal investigations'. (Arthropods belong to a group of animals that includes spiders, crabs, scorpions and centipedes, as well as insects).

Forensic entomologists are usually attached to a college or university department, although some will be employed at a museum of natural history.  A forensic entomologist's caseload would not usually justify a position in a forensics laboratory.  Forensic entomology is mainly a sideline to the teaching and research duties of their regular job.

 

There are three major branches of forensic entomology.

 

1. Medico-Legal (Medico-Criminal) Entomology

 

This branch is concerned with the investigation of mainly criminal cases, particularly homicide.  The bulk of the work of the forensic entomologist will involve determining the Post-Mortem Interval (sometimes called 'elapsed time since death') or site of death.  The Post-Mortem Interval is the time between death and the discovery of the body.

Other cases may involve the criminal use of insects, such as when a parent deliberately stings their child with a wasp or bee as a form of punishment.

In cases of unexplained death, where the corpse is too decomposed for the analysis of stomach contents, urine or blood, it is possible to analyse maggots, empty puparia (cases that contained the pupae) or larval skin casts in or on the corpse for evidence of poison.

When investigators need to know the route taken by a car - and there is no GPS navigation device in use or CCTV evidence - a forensic entomologist may be called in to examine the fragmented remains of insects that have become splatted against the windscreen, front fascia and radiator of the vehicle.  Identification of the insect species can provide evidence of the probable passage of the car through a particular area.

2. Urban Entomology

This branch deals with the insects that affect both man and his immediate environment.  The legal proceedings may be heard in either the criminal or civil courts, depending on the case e.g. monetary damages cases will be civil proceedings.

Examples include problems with cockroaches, termites and other pests, insect nuisance from agriculture and neglect cases involving insect infestation of patients in hospitals and care homes.     

3. Stored Product Entomology

This branch is mainly concerned with civil disputes involving insects and other arthropods in food and stored products, but can also include criminal investigations.. 

Different species of arthropods may often be found together in stored containers of illegal drugs.  The drugs are most likely to have been manufactured in one country and sold in others.  If a forensic entomologist identifies the arthropods and then plots their world distribution on a map, any areas of overlap between the species can indicate, approximately, where the drugs might have come from.

Further study of the biology of the identified arthropods may provide information on the surroundings in which the drugs were produced or packed.

Stored Product Entomology also covers cases of fraud where insects have been deliberately introduced into packets of food with the aim of claiming substantial 'compensation'.       

Whilst there are a lot of fascinating cases involving insect evidence - which I can come back to in other blogs - I want to concentrate on the use of forensic entomology to establish the Post-Mortem Interval (PMI), since this is the major area of a forensic entomologist's expertise.

The lure of a decaying corpse

As far as an insect is concerned, a human corpse is a piece of carrion which provides the perfect medium for feeding and reproduction.  Although a wide variety of insects will be attracted to the decaying remains, flies are the most important group from a forensic entomologist's viewpoint.

A forensic entomologist will not need to be called in to assist an investigation until the body is 72 hours or more old.  Up until this point, other forensic methods are either equally or more accurate than insect evidence.  However, after this time, insect evidence may be the only method of determining the PMI.

How to determine the Post-Mortem Interval

There are two methods of determining the PMI.

1) Using Successional Waves of Insects

This method is used when the corpse has been dead between a month and up to a year or more.

During decomposition, the remains go through a variety of biological, chemical and physical changes.  Different stages of the decomposition are attractive to different species of insects.

The first insects to arrive are the blowflies.  They can arrive within 24 hours of death if the season is suitable. 

Other species are not interested in the fresh corpse.  Cheese skippers, a worldwide pest of cheese and bacon, will arrive between 3 - 6 months after death, during protein fermentation.  Beetles that feed on bones will not arrive until the bone is exposed.

Some insects are not attracted to the body itself, but feed on the insects already present.

Ultimately. there will be many species involved at each stage of decomposition.  Each group of insects will overlap with those arriving immediately before and after. 

The forensic entomologist will therefore analyse the groups of insects that are associated with the corpse.  He or she will also need knowledge of the local insect population, as well as knowledge of insect succession and the times of carrion decomposition.

Having all this information in place will allow the forensic entomologist to determine a window of time in which death took place.

2) Using Maggot Age and Development

This method can allegedly give a date of death accurate to a day or less, but more likely a range of days.  It is used in the first few weeks after death.

The theory behind estimating PMI is simple.  Since insects arrive on the body soon after death, by estimating the age of the insects on the corpse, it is possible to estimate the time interval since death.

Maggots are the immature stages of the Diptera or two-winged flies.  The maggots of forensic interest are those of the Blowfly, the first insects to arrive on the dead body.

Here is a  slightly grisly video, explaining the importance of blowfly maggots when estimating the PMI.

As mentioned in the video, each of the developmental stages in the blowfly's life cycle takes a known time.  This is dependent on temperature and available food (not usually a limitation where a corpse is concerned).  Development takes longer in cooler temperatures.

Here is the basic procedure from call-out to a corpse to estimation of the PMI.

1) Collecting, preserving and packing specimens

Samples of insects at all stages of their life cycles are collected from the body, but the maggots are the most important.  Wounds and natural orifices are particularly good collection areas.  Insects should also be collected from clothing, coverings and the surrounding soil, for example.

Some samples should be preserved in 75% alcohol; the remainder should be kept alive for growing on in the laboratory.  Preserving the maggots, etc. allows the entomologist to keep an accurate record of the stage that they were at when they were collected.

Here is a video showing the type of equipment used at crime scenes to collect insects.

The samples are packed in cardboard boxes with a good air supply and taken to the entomology laboratory.

In addition to collecting samples, the forensic entomologist must make extensive notes about the habitat of the death site, take the temperature and humidity at the time of collection and assess the weather conditions.  The elevation and map coordinates of the death site must also be noted.

He or she must also make detailed records about the corpse, such as whether or not clothing was present, was the body buried or covered, depth of burial or covering, location and type of wounds, state of decomposition, how many maggots are present (if any) and whether the body been moved to this site after death.

2) At the entomology laboratory

When the live maggot samples arrive, they will be measured and examined and then placed in a jar with some food, such as beef liver.  The food is placed on top of some sawdust; the maggots will burrow in the sawdust to pupate.

When they pupate, they are taken out of the sawdust and placed on damp filter paper in a petri dish.

The forensic entomologist notes down when pupation occurs and how long it takes.

When the adult emerges it is killed and pinned and placed in an insect box.  The same fate happens to any adult flies collected directly from the corpse.

It is only when the collected eggs or maggots have developed into adults that the forensic entomologist can be absolutely sure which species have/has colonized the corpse.

3) Estimation of PMI

The estimation of PMI is based upon direct age assessment of the oldest specimens developed on the body. 

By relating maggot development to local climatological data from the period prior to the discovery of the corpse, the forensic entomologist can estimate the number of days that it would take for the maggots to reach the size and stage found on the remains.

This time period is the PMI.

Here is a video showing more maggots and pigs carcasses, but it has some good time-lapse photography.

I'll leave you with a video showing 'celebrity' forensic entomologist, Dr Lee Goff, talking about his work. 

Forensic entomology is a huge subject and this blog has only scratched the surface.  I plan to re-visit the subject soon.

Don't forget to leave a comment and a link to your book.