At the present stage of development of society, there is a negative trend towards an increase in the level of crime in our state. Effective, quick and complete investigation of crimes and bringing the perpetrators to justice is primarily ensured by the quality of the pre-trial investigation and the availability of an appropriate evidence base.

Obtaining samples for fingerprinting, phonoscopy, forensic and other types of examinations is almost impossible without the involvement of a specialist. The legislator procedurally regulated the ability to involve a specialist in the selection of samples for examination and left the right to choose on the side of the criminal proceedings, which filed a petition for the necessary examination.

The samples used for comparative research are objects (substances and (or) objects), including their physically fixed representations, containing a set of features of specific objects, including persons, subject to comparative research. In the process of implementing a forensic examination, samples for a specific comparative study are used by the expert conducting the study as necessary materials for comparison, but at the same time “for the investigator, they are subject to all the requirements for proof in working with evidence” [2].

Bravilova E. A. notes the requirements that samples must meet for all types of research, namely: legality, reliability, comparability and sufficient quantity [1]. Also, there is no classification of samples in the legislation, which is important for the study.

The Decree “On Forensic Examination in Criminal Cases” defines the types and concept of samples for specific studies [4]. After analyzing the scientific literature and current legislation, in general, the following types of samples can be distinguished: free, conditionally free and experimental.

A person from whom samples are taken specifically for examination can consciously change his specific properties and characteristics. Undoubtedly, this complicates the examination. «These materials were written by a person who is being checked before the opening of criminal proceedings and have no connection with him» [3].

Objects that are used as conditionally free “appear after the opening of any criminal proceedings, but are not related to the preparation of materials for examination” [5]. Samples that arise after the opening of criminal proceedings are called experimental, since appropriate conditions are usually created to obtain them. Together with the generally recognized appearances of the samples, the following: reference, samples of «materials or substances of the object under study, control and collection» [2].

To solve research issues in ballistic examinations in the examination of edged weapons, the latter is used. They should include books, albums, reference books of vehicle tread patterns, cold steel and firearms.

Such samples simplify this work of an expert, for example, when identifying a modification and brand of a foreign pistol with an obliterated marking, and in other cases [3]. Reference samples help to solve both classification and diagnostic issues.

Namely, when designating the brand of oil products, paintwork material, the name of poisonous or drugs. They are necessary in case of establishing the fact of diluting «expensive» gasoline with «cheap» one, counterfeiting alcoholic beverages, etc. [1].

Standards of materials or substances of the object under study, «depending on the situation, can take part in the form of an average sample for watery and unsteady substances, as well as sample-authorized persons of the whole» [4]. Trial samples are usually used in forensic examination of materials and substances, technical examination of documents, examination of soils, forensic bio examination of objects of animal and plant origin, etc.

They are confiscated in order to verify the properties of the object. These samples are used for control, in the examination of soils they are called soil samples. According to them, the boundaries of the territory into which the place of the criminal act enters are calculated. Earth samples are taken both from the scene itself and beyond [3]. This classification of samples for examination, like any other, is conditional.

However, applying these provisions, it can be argued:

1. Only the investigator seizes free and conditionally free samples.
2. Collection and reference samples are also selected by an expert. This state of affairs is due to the fact that when conducting identification ballistic, investigative and some forensic medical examinations, the assignment of samples for comparison is the function of an expert, since this is one of the stages of a comparative study.
3. Experimental standards are also selected in the same way, however, the samples that are obtained in the process of comparative analysis are selected by a specialist alone.
4. Samples of materials and substances of the investigated object are taken by the investigator.

If the provision of samples from the object sent for comparative analysis is carried out in the process of examination, then such an action is carried out by the expert himself, and the procedure for obtaining such samples should be reflected in the expert’s opinion [3]. It is clear that at the legislative level it is impossible to provide for all cases when it is necessary to involve a specialist to carry out these investigative actions, since various situations arise in practice.

However, it is worth highlighting the main factors that determine the feasibility of involving and the role of a specialist in obtaining samples.

1. If a qualified investigator can independently take experimental samples for handwriting examination, then when selecting samples for soil science examination, it is advisable to involve a specialist, since such an investigative action requires special knowledge.
2. If obtaining free and conditionally free samples in most cases does not require special skills, then when obtaining experimental samples, the investigator must be aware of the features of the selection of such samples or involve a specialist. Samples (samples) of materials and substances, as a rule, are taken with the participation of a specialist, which is due to the complexity of these procedural actions and the need for special knowledge.
3. Investigator skills. Skilled sampling depends on the experience and knowledge of the investigator. However, this is not a decisive factor. The investigator who studied the course of criminology, has mastered only the minimum knowledge provided by the program in criminology for law schools. It is clear that the specialist has in-depth knowledge of all branches of forensic science and knows forensic technology at the current level of development.

The selection of materials for examination requires the necessary knowledge of the methods of comparative research, compliance with the rules for extracting, packaging and storing objects of comparative research. The implementation of such actions by the investigator independently bears certain risks for future examination.

Therefore, the involvement of a specialist in obtaining samples and preparing samples for comparative analysis is justified, first, by the difficulty of selecting samples for certain types of examinations, the types of samples that need to be obtained, and the level of training of the investigator. Based on the analyzed material, it can be argued that the use of special knowledge at this stage of the pre-trial investigation contributes to the qualified implementation of such actions.