The present paper arises from wider research which focused on various manifestations of destructive and malicious speech behavior in spontaneous oral or written dialogs, related to the processes of information concealment and falsification in police interviews and court testimonies. A number of analytical methods were used to generate this paper: a retrospective analysis of scientific literature, comparative legal and logical analysis, extrapolation methods, and content analysis. Despite numerous experimental researches devoted to acoustic-phonetic or psycholinguistic features of lies, their results are not sufficiently reliable for forensic purposes as the expert report should not rely on assumptions. The author disputes the evidence admissibility of experts’ conclusions about utterances implying speech parameters correlating with lies detected via psycholinguistic examination in oral speech audio or video recording of a police interview or a court testimony. Forensic psycholinguistic methods and comprehensive algorithms used in some forensic experts’ reports to detect speech signs of lying demonstrate a great variety that contradicts with the principals of evidence admissibility. The insufficient development of the currently used expert approach and the lack of a unified methodology for solving expert tasks on a strictly scientific basis creates a demand for developing comprehensive methods for studying lies on the basis of forensic speech science and cognitive theory.