It's a Jack the Ripper mystery solved. Unfortunately that's "a" mystery, not "the" mystery. A forensic linguist with the UK's University of Manchester says that after learning no forensic linguistic analysis had been carried out on any of the letters purportedly written by the infamous murderer, he decided to examine two of the most famous ones and has determined that the two were penned by the same person. More than 200 letters from "Jack the Ripper" were sent in the wake of the 1888 deaths, and as Dr. Andrea Nini's paper in Digital Scholarship in the Humanities explains, "The most supported theory ... is that some of the earliest key texts were written by journalists to sell more newspapers and that the same person is responsible for writing the two most iconic earliest letters."
Nini writes that he carried out a "cluster analysis" on 209 letters and found "very strong linguistic evidence" that those two iconic ones—the "Dear Boss" letter that was the first to include the name "Jack the Ripper," and a postcard that refers to the killer as "Saucy Jacky"—were indeed written by the same person. While Nini says others have come to that conclusion based on handwriting analysis, his was the first to establish this "with certainty." A press release gives one example of the evidence: "use of the phrasal verb to keep back (to withhold)," described as a "distinctive linguistic construction." Nini also found that a third letter, the Moab and Midian letter that was thought to have been the work of the Central News Agency of London, was also likely written by that same person. (Was Jack the Ripper a wealthy cotton merchant?)