応用言語学の1分野として法言語学 (forensic linguistics) があります．昨日の朝の Voicy 「英語の語源が身につくラジオ (heldio)」で「#660. 「法言語学」 (forensic linguistics) とは？」として紹介しました．さらに夜の YouTube 「井上逸兵・堀田隆一英語学言語学チャンネル」で「#112. 商標の言語学 --- 五所万実さん登場」として，関連する話題について井上氏および五所氏と雑談しています．ぜひ聴取・視聴していただければ．
いくつかの用語辞典で "forensic (socio)linguistics" を引いてみました．以下，3点ほど引用します．同分野の守備範囲がおおよそ分かってくるかと思います．
forensic linguistics In Linguistics, the use of linguistic techniques to investigate crimes in which language data forms part of the evidence, such as in the use of grammatical or lexical criteria to authenticate police statements. The field of forensic phonetics is often distinguished as a separate domain, dealing with such matters as speaker identification, voice line-ups, speaker profiling, tape enhancement, tape authentification, and the decoding of disputed utterances. (Crystal, Dictionary)
forensic sociolinguistics The use of sociolinguistic knowledge and techniques in the investigation of crime, and in the prosecution and defence of people accused of crimes. Sociolinguists have been employed, for instance, to demonstrate that a defendant could not have made a telephone call recorded by police because his dialect did not tally with that on the recording; and to decode recordings of communication between criminal speaking in an antilanguage such as Pig Latin. (Trudgill)
Most stylostatistical studies are of literary works; but the same techniques can be applied to any spoken or written sample, regardless of the 'standing' of the user. In everyday life, of course, there is usually no reason to carry out a stylistic analysis of someone's usage. But when someone is alleged to have broken the law, stylisticians might well be involved, in an application of their subject sometimes referred to as 'forensic' linguistics.
Typical situations involve the prosecution arguing that incriminating utterances heard on a tape recording have the same stylistic features as those used by the defendant---or, conversely, the defence arguing that the differences are too great to support this contention. A common defence strategy is to maintain that the official statement to the police, written down and used in evidence, is a misrepresentation, containing language that would not be part of the defendant's normal usage.
Arguments based on stylistic evidence are usually very weak, because the sample size is small, and the linguistic features examined are often not very discriminating. (Crystal, Encyclopedia)
・ Crystal, David, ed. A Dictionary of Linguistics and Phonetics. 6th ed. Malden, MA: Blackwell, 2008. 295--96.
・ Trudgill, Peter. A Glossary of Sociolinguistics. Oxford: Oxford University Press, 2003.
・ Crystal, David. The Cambridge Encyclopedia of Language. Cambridge: CUP, 1995. 2nd ed. 2003. 3rd ed. 2019.