From Hell letter
Many letters that were claimed to be from the killer were mailed in the time of the Ripper murders. But the "From Hell" letter is thought as one of the few writings from the serial killer. It should be noted that its author chose not to sign it with the pseudonym, "Jack the Ripper", distinguishing it from the earlier Dear Boss letter, the Saucy Jack postcard and their imitators.  Also, the "From Hell" letter is written at a much lower literacy level than the other two. It is argued that a person with little or no education would spell words based on what they sound like and as the 'k' in knife is silent, an uneducated man would not likely know that the 'k' was there at all.