What laws should be cited in order for the police to invite witnesses?

Part 7 of Article 223 of the Criminal Procedural Code of Ukraine establishes: the investigator, the prosecutor is obliged to invite at least two disinterested persons (understood) for presentation of a person, corpse or thing for identification, examination of a corpse, including exhumation, investigative experiment, examination of a person. Exceptions are the cases of continuous video recording of the course of the corresponding investigative (search) action. Subjects may be invited to participate in other procedural actions, if the investigator, prosecutor considers it appropriate.

If a police officer deliberately did not comply with the above-mentioned article, you should inform his supervisor about it.