I do not believe that any of the infamous letters were written by the perpetrator. Although the name, “Jack the Ripper”, originated from one of these letters (Dear Boss), it is likely that the assailant did not even give himself this name.
Several reasons exist for this rationale. First, very little evidence exists to suggest that the actual ripper wrote any of the most infamous letters. After the murders, police stated that the ‘Dear Boss’ letter and ‘Saucy Jack’ postcard was most likely written by an overzealous journalist. Similarly, the “From Hell” letter, contains little evidence that can tie it to the ripper himself. The misspellings appear as if they were written by someone attempting to seem uneducated. For example, an uneducated person would not spell ‘knife’ as ‘knif’ but would most likely spell it without the silent ‘k’ (nife). Also, there is no evidence that the kidney sent with the letter is that of the previous victim, Catherine Eddowes.
Secondly, the modus operandi of the perpetrator indicates that all his attacks were generally disorganized patterns of killing. The FBI’s criminal profile of the case indicates that due to the location of the crime, blitz attack nature, and abandonment of the bodies, the ripper was lucky rather than clever. Few disorganized perpetrators desire to attract further attention to their crimes from the media or police. Thus, the type of murder seen in the Whitechapel district demonstrates the unlikeliness that the ripper would have written a letter glorifying his crimes.