Survey of nicotine scent on correctness of special dog’s indications in human scent traces identification

One of the problems encountered by the experts performing osmological examination is a question whether dogs might follow components of “scent molecules”1 other than an individual scent.

In particular,  scents of cosmetics2, alcohol and nicotine can evoke doubts. Since a population of smokers, is unfortunately quite big, a question arises whether  smoking habit of a person can significantly influence the results of investigation. If so, should such information be included in a specification of comparative materials and of complementary materials in an identification line-up.

At an early stage of applying scent identification in forensic examination, smoking was banned not only in a scent identification room, but also in its surroundings and dog handlers were not allowed to smoke in certain time preceding a work with the dog. In addition to this, a use of wooden holders for cigarettes was required.

Paradoxically, it was recommended to recover cigarette-ends for the scent identification examinations and what is more, some positive results were obtained from the identification of such traces3.

It is now known from practice (experience of dog handlers and experts performing scent identification examinations), that the fact of smoking or non-smoking has no influence whatsoever on the examination results. And yet, this conviction of dog handlers and experts in scent identification could not stand for a scientific argument. That is why it has been decided to experimentally examine the influence of nicotine scent on the correctness of indications of dogs identifying human scent traces.

 Materials and methods

 Two sets of scent samples from students of CSP in Legionowo Police Training Centre were  recovered in special containers. These students were divided into two groups:

1) non-smokers sharing rooms with other non-smokers,

2) mokers of 20-30 cigarettes a day – there were no pipe or cigar etc. smokers in that group.

 From each student, comparative scent samples from clean hands were collected onto 18 TZMO absorbers (3 containers) and 12 “evidential” material samples (2 containers) were collected from clothes.

28 special dogs were used to identify scent traces (the dogs staying at Zakład Techniki Kryminalistycznej CSP at refreshment courses, and dogs trained at SEI course – at a final stage of training).

Each dog, directly before the proper examination, was subject to a control test in order to check if:

1) Any complementary material (selected according to standing rules) was not attractive for a particular dog.

2) Comparative material was not attractive to the dog.

3) The dog was fit for work on that day.

The materials “attractive” for whatever reasons for one dog were completely excluded from the experiment. The results of control tests were not included in a description for a sake of chart clarity.

Only the results of 10 best dogs were considered in the experiment, i.e. those, who performed the control tests properly and worked without visible fluctuations of form. All the dogs included in the chart were given the certificates qualifying them to perform osmological examinations to be used in investigative proceedings.

In order to avoid false positive indications each kind of material, i.e.:

a) comparative material from the non-smokers,

b) “evidential” material from the non-smokers,

c) comparative material from the smokers,

d) “evidential” material from the smokers

were recovered by different technicians and labelled with first names. Only leader of the examination knew to which scent group each container should be attributed. Dogs handlers treated the collected materials as regular practice materials – they were not informed of taking a part in the experiment.

An instructor leading the training  supervised the setting of the identification line-up, so that it was compliant with the assumptions of examination; he controlled the course of experiment and its results.

In no case were the dog handlers informed about a position of comparative material in the identification line-up, nor they knew where the examined – experimental material was placed.

All the comparative and complementary materials corresponded with one another in terms of groups.

 Course of the examination

 There were two experimental set-ups prepared for the experimentation.

In the first set-up, a dog was given the “evidential” material coming from a smoker (MD-P) to be sniffed at. In the identification line-up there were additional materials (MU-N), collected from non-smokers, one additional material collected from a smoker (MU-P) and also a comparative material from a smoker (MP-P) of a scent matching the evidential material.

That is to say:

MD-P = MP-P,

and MD-P and MP-P ≠ MU-P and MU-N

where:

(=) a scent match is present,

(≠) an absence of scent match.

 The line-up was always composed in accordance with the assumption, that the examined material (MU-P) was placed in the identification line-up in a position preceding the comparative material (MP-P). The kind of set-up was each time chosen at random for each dog, but it had to comply with a specification presented below (Table 1).

Independently of a chosen material, a correctly working dog should indicate comparative material collected from a smoker (MP-P). Indicating of an additional material collected from a smoker (MU-P) would prove, that the material (in spite of control tests) is attractive for the dog – that would mean that the dog is driven by the scent of nicotine and not by the individual human scent (Table 2).

In the second experimental set-up an opposite scheme was applied, i.e.:

A dog was given the “evidential” material collected from a non-smoker (MD-N) to sniff and in the line-up it had to search for the comparative material from the same person (MP-N). That is:

 MD-N = MP-N

 In the identification line-up there were some complementary materials collected from smokers (MU-P) and one complementary material collected from a non-smoker (MU-N), with no scent match with evidential (MD-N) or comparative material (MP-N) – Table 3 and therefore:

 MD-N and MP-N ≠ MU-P and MU-N

 where:

(=) presence of scent match,

(≠) an absence of scent match.

 Set-ups chosen at random were applied identically as in Table 1.

 Results and conclusions of the examination

 As a result of the carried out examination it was concluded, that in case of 50 examinations (150 actual tests) in the identification line-ups, when the dog was sniffing at and then was to find the materials collected from smokers, and when in the identification line-up there was one additional material collected from a smoker amongst the materials collected from the non-smokers, there was one false indication in one actual test (1 test out of 150). In three different tests (3 tests out of 150) the attractiveness of the additional material collected from non-smokers was indicated. After removing these materials (not indicated in the control tests), the dogs performed all the remaining examinations correctly.

In the second, opposite experimental set-up (also a number of 50 examinations and 150 actual tests), only one mistake occurred, at a time directly preceding a refusal of further work, and one case of a refusal of further work after having correctly performed the control tests.

Having analysed the above results, it can be observed that:

1. Smoking habit by persons being subject to the osmological examinations does not influence the correctness of indications by dogs, independent of the applied variant of examination.

2. There were no critical differences in dog performance depending on the fact whether the dog handler was a smoker (dogs no. 1-6) or not (dogs no. 7-10).

3. The scent of tobacco can only make the work of dogs difficult (in the extreme cases they refuse to work), but it can not influence the correctness of their indications.

4. There is no need to note down in specifications of the scent containers of comparative and additional materials the fact of smoking, since there is no necessity of composing separate identification line-ups for smokers and non-smokers.

Krzysztof Misiewicz

prace badawcze