Who What Why:
How durable is a fingerprint?
28 September 2012 BBC News
How durable is a fingerprint?
28 September 2012 BBC News
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| The three main fingerprint types - the loop, the whorl and the arch |
American Hans Galassi
lost several fingers in a wakeboarding accident several months ago. Now one of
them has been found in a trout - and identified as Galassi's from its
fingerprints. So how long do fingerprints last?
The vast majority of
people are born with a unique set of fingerprints which remain the same for
life.
These patterns, known
as friction ridges by experts, are found not only on our finger-tips but also
on the flanges of our fingers, on our palms, our toes and on the soles of our
feet.
The patterns are
permanent, but can wear down. Builders who lay bricks and people who frequently
wash dishes by hand lose some of the detail. Once they stop these activities,
the ridges will grow back.
As fans of crime
movies will know, from time to time people have tried to change their
fingerprints patterns artificially.
A deep cut through the
outer layer of the skin, the epidermis, and down to the dermis leaves a scar
that will change a fingerprint, but not make it any less unique.
People have also
sought to erase their fingerprints by burning the finger-tips with fire and
acid, as the notorious 1930s American gangster John Dillinger did. It works for
a while but the skin grows back.
Another criminal, Robert
Phillips, famously grafted skin from his chest on to his fingers to erase his
fingerprints - but he was identified from the prints of his palms. Others have
tried smoothing their finger-tips with glue and nail varnish. Again they were
caught from palm prints.
Friction ridges are
remarkably long lasting even after death, says fingerprint expert Allen Bayle,
author of the UK's standard police manual on dead hands.
"If a hand is
found in water you will see that the epidermis starts to come away from the
dermis like a glove. This sounds gruesome but if a hand has been badly damaged,
I cut the epidermis off and put my own hand inside that glove and try to
fingerprint it like that," says Bayle.
"Some boys we get
out of the water, the fish have been at them already and the fish will have
pecked at the epidermis. But you can still get ridge detail from the underside
of the epidermis. And if that has gone, then you can do the dermis. For every
ridge you have on the epidermis, you have two on the dermis - we call it a
tramline effect."
The speed at which a
hand disintegrates in water depends on many things, not least the temperature
of the water itself.
"If the water is
very cold, it could stay for a long time," says Bayle. And the body of a
trout, the fish that swallowed Galassi's finger, is just as cold as the water
it swims in.
Galassi's finger was
found in the trout's digestive tract - why hadn't it been digested? We shall
never know how long after the accident the fish ate the finger, but Bayle
thinks even if the thick layer of epidermis had been digested, Galassi's finger
could still have been identified from its dermis.
"We can cast [the
finger], for example in latex, and then we can ink the cast. Or we can ink the
dermis and roll it on a fingerprint form. When we have got some ridge detail
then we can put it on the computer."
In the case of
Galassi, Idaho police took a day searching case files and reports to narrow
down where the finger could have come from. They then fingerprinted the stray
digit and sent it to the state police forensic lab where technicians were able
to identify its owner.
"One of the last
things to disappear when you die are your fingerprints," says Bayle.
"They're very durable."
More: BBC News
Peter’s Piece
The best way to avoid arrest is to stay out of crime,
and even that is no guarantee. So the best, best, best way is to stay home with a good book. But be really careful because books can contain ideas for the perfect crime.
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