In this first of a series of a new
“Shoulder Strap” feature, Sergt. Carl
Ledoux of the Criminal Investigation
Branch, conducts a question box for
the scientific investigator.

Q. WHERE AN object on which a finger-
print has been left is too heavy to present
in court, or the print inaccessible to a cam-
era, can the print be “lifted” and is this
good practice?

A. There are materials on the market for
lifting latent fingerprint impressions where
this situation is encountered. The principle
is to “lift” the print after powdering it,
then photograph it.

While the system may have some prac-
tical advantages there are also some disad-
vantages. There may be a certain amount
of stretch to the lifter which will distort
the print. Then again the article from
which the print was lifted is valueless as
evidence. Another disadvantage is that the
only proof that the particular lift came from
a certain article is the recollection of the
fingerprint operator and his notes. In a case
where a number of lifts had been made there
might be serious doubt as to which lift
came from which exhibit. And last but not
least is the fact that there is a serious loss
of detail in lifting.

Our best advice is, after development,
latent prints should not be tampered with.
They should be photographed and the orig-
inal print preserved by storing the article
or if the surface cannot be detached, build
a wood or cardboard “‘guard” contrived to
cover the print so that nothing can touch it.
This is particularly true if a person has
already been charged and is awaiting trial.

“Lifting” has been suggested for those
hard-to-get-at places where the ordinary
fingerprint camera is at a disadvantage;
however, our Criminal Investigation Branch
has worked out a new technique for hand-

TWELFTH EDITION

ling this situation. By using a prism over
a camera lens photographs can now be
taken at right angles to the surface.

* * *

Q. How do you take a cast of a footprint
in snow?

A. First you must take into consideration
the type of snow in which the print is made.
If it is dry and powdery there is little chance
of success. The slightest movement will
cause the powdered snow to fall into the
print and there is very little chance that
the print will be clear enough to warrant
casting. It might be of use in determining
approximate dimensions but little else.

Snow with a crusted surface also presents
difficulties as the crust merely breaks and
forms an irregular base to the print which
carries very little detail. However, the cast
may be of help in determining general
dimensions.

Best chance of success is with wet or
damp snow which is capable of hard pack-
ing. You can get good results with a little
practice and the exercise of a little care.
Even fairly dry snow can at times yield
fairly good prints as the compressing weight
of the foot or tire causes momentary melt-
ing and forms a thin film of water at the
base of the print which freezes when the
weight is removed. This thin layer of ice
helps preserve the print until thawed out.

Some investigators have been successful
in making snow prints using a water and
plaster of paris mixture the consistency of
thick cream. Allow to thicken slightly be-
fore pouring into the print. The thicker
the plaster the less detail you will get. A
disadvantage is that plaster of paris gives
off considerable heat while setting and this
will naturally affect the casting quality.
When using plaster of paris in this fashion
be sure to break the fall by a stick or board
as you pour the mixture into the print.

The best method of treating snow prints
is by the shellac-resin method. Finely pow-
dered resin is carefully sifted or blown on
all surfaces of the print to form a fine layer.
Then use a mixture of shellac and alcohol
in a fly-spray gun all over the print. The
resin will then be bound by the liquid shel-
lac. After an interval to allow the shellac
to dry blow on a second layer of resin, and
repeat the application of shellac. The more
care that is used and the finer the initial
layer, the better the detail. After you get
a good cast you can fill it with plaster of
paris mixture. You can reinforce the plaster
cast by including a few pieces of plaster-
soaked cloth, pieces of string, sacking, etc.

One point should not be overlooked: if
the print is worth making an attempt to
preserve, then take a photograph of it before
attempting any casting. In the event the
cast fails, you still have the photograph. Be
sure to have a ruler alongside the print in
your photograph.

Q. Can you describe a simple field test
for blood stains?

A. The most widely used test involves
the use of the reagent benzidine. It is quite
accurate and requires little technical skill.
It is handy for the rapid elimination of
worthless evidence, but if a positive result
is obtained do not regard the test as final
proof. Only a properly equipped lab. can
do this where a series of different tests are
applied to eliminate any chance of error.

You will require the following materials.
benzidine or benzidine di-hydrochloride,
glacial acetic acid and hydrogen peroxide.
The kenzidine is dissolved in the glacial
acetic acid with the addition of a little
water. The quantities are not critical.

_ Apply the solution to a particle of solid

material on a piece of white blotting paper.
If there is some blue colouring then the
subject under test is one of the few which
react to bendizine other than blood. If
there is no reaction at this stage, apply hy-
drogen peroxide. If again there is no visible
reaction the substance is not blood, but if
the paper shows a blue stain within a few
seconds then it is almost sure to be blood.

Be sure to exercise care not to use up all
available material in your test, for even if a
positive reaction is obtained your theory will
have to be confirmed by laboratory analysis.
If there is any doubt in your mind that you
may endanger the only available sample by
making a field test, then refrain from any
action and send the sample at once to the
analyst. Remember your test alone is not
sufficient for court purposes.

TOM BERTRAM, Pharmacist

LADYSMITH DRUG STORE

Phone 26 Ladysmith

for

A Complete, Modern Drug Service

Hotel

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THOMAS STEVENSON, Manager
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Page Seventeen