So who did nibble Santa’s mince pie?

GRAHAM WILLIAMS, a lecturer in forensic science at the University of Huddersfield, takes a festive look at the work of Crime Scene Investigators

As we enter the month of December, our thoughts inevitably turn to Christmas. One of the many questions that often preys on our mind is ‘Who nibbled Father Christmas’ mince pie?

This sorrowful story of a part-munched mince pie is one that has baffled him for many years. After a hard slog around the globe on Christmas Eve, Father Christmas likes to settle down in front of a roaring log fire and have a nice mince pie. But every year, he finds a bite sized chunk in the Christmas treat.

This continued for many years until Father Christmas got very cross and called in CSI: North Pole. The CSIs duly sealed off the crime scene; donned the white crime scene suits. They promptly then removed the white scene suits and put on blue ones as they could not see each other in the snow!

They entered the crime scene and recovered the remains of the nibbled mince pie. The pie was then placed in a cardboard box and packaged so the pie would not be destroyed in transit.

The cardboard box was then sealed in a police evidence bag and labelled with the date and time of recovery and who recovered it. A record of the item seized along with the unique serial number of the police evidence bag would be entered into the crime scene report.

This represents the start of the “chain of custody” of the nibbled mince pie. Without this chain of custody, any evidence obtained from the mince pie would not be admissible in a court of law.

The CSIs also examined the floor surrounding the nibbled mince pie and they noticed a series of what appeared to be footwear marks.

On closer inspection, these turn out to be hoof marks. Specifically, reindeer hoof marks. The CSIs now have nine suspects; Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Donner, Blitzen and Rudolph.

How can we work out which of the reindeer is the nibbler? In this particular case, there are three things we can look at. Teeth marks in the nibbled mince pie, comparing the hoof marks with each of the reindeer’s hooves and reindeer DNA recovered from the edges of the bite in the mince pie.

It is possible to link a bite mark from a bitten item with the teeth of the biter; however, this depends on distinguishing characteristics present in the teeth.

This has been done successfully in the past, where bite marks on skin has been matched to someone’s teeth and where a bite out of a piece of cheese or apple at a scene of a burglary has been linked to a suspect.

However, Father Christmas takes very good care of his reindeers so they all have very healthy teeth and the bite marks were not capable of distinguishing between the reindeers.

We could try comparing the hoof marks with the hooves of the reindeer. So, photos of the hoof marks were taken. Each of the reindeers was asked to provide their own hoof marks to the CSIs, who then carried out a comparison.

Examples of distinguishing characteristics can include the size of the hooves, the shapes and any damage. In this notorious case, they were unable to identify any one reindeer, but they could eliminate Dasher and Dancer.

Both Dasher and Dancer had significant wearing to the front of their hooves as they would usually be at the front of the pack; therefore, when they land on the roof of the houses, they take the brunt of the impact.

So we are now down to seven suspects. The next thing left is reindeer DNA profiling.

The edges of the bite marks on the nibbled mince pie can be swabbed and saliva can be recovered.

The saliva contains cells from inside the mouth. DNA can be extracted from these cells and then profiled. A reindeer DNA profile was obtained from the saliva recovered.

Each of the seven remaining suspect were then asked to provide a reference DNA sample by swabbing their own cheeks (actually, the CSIs did this as it is difficult for reindeers to hold a swab). Everyone’s DNA is unique (except for identical twins), therefore it is possible to eliminate suspects using DNA profiling.

In this case, Prancer, Vixen, Comet, Cupid, Donner and Blitzen were eliminated from having contributed to the DNA recovered from the nibbled mince pie.

The DNA profile matched that of Rudolph. Based on this, Rudolph was interrogated and he confessed to nibbling the pie...