One source of data for the forensic linguist is the extortion note - but when the alleged extortioner marks the letters "Ëxtortion Notice" and does little to hide his identity, there is (sadly for us) no need to call in a forensic linguist.

http://www.dailymail.co.uk/news/article-2211855/Vivek-Shah-Indictment-shows-actors-chilling-extortion-threat-victims-like-Harvey-Weinstein.html

Part of the indictment (from TheSmokingGun)