The Riverbanks Ripper was a serial murderer, who killed nine people in the 1970s. He was never identified. At one of the crime scenes he left behind an encrypted note that is unsolved to date.

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The Riverbanks Ripper was one of the most dangerous serial killers in US history. After his first murder in Geneva, Illinois, in November 1970, he committed eight more brutal homicides until 1980. In 1976 the FBI published the following identikit based on the decriptions of several eye witnesses:



The Riverbanks Ripper cryptogram

When on April 1st, 1975, the Riverbanks Ripper murdered his fifth victim, he left behind a piece of paper bearing an encrypted message. This cryptogram has never been solved. The Riverbanks Ripper cryptogram is pretty short, consisting of only one character. Here it is:


The single character the Riverbanks Ripper cryptogram consists of can be interpreted as a capital I. However, it could as well be an “l”, a “1”, or an incomplete “T”. When the sheet is turned by 90 degrees, this symbol can also be read as a dash, a hyphen, or a Morse code “T”.

Several transcriptions of the Riverbanks Ripper cryptogram have been published. The one I like best was created by blog reader George Fabyan in 2013. Here it is:



Even the best experts have failed

Based on George’s transcription we can conduct a frequency analysis:

0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

The tool CrypTool Online renders the following diagram:


I find it especially interesting that the variance has a value of 369.82249, which is exceptionally high. I would have expected at most 360. The standard variation (19.23077) is above average, too. In my view, only a prefessional cryptologist can develop an encryption method having such peculiar (and probably misleading) statistical properties.

Dozens of renowned codebreakers have tried to solve the Riverbanks Ripper cryptogram, but so far nobody has come up with a convincing solution. While some experts believe that the Riverbanks Ripper used a multiplicative cipher, others think that a substitution permutation network fits better with the statistical properties of the ciphertext. In my view, even a Feistel cipher, which was a quite new technique at he time, is an option.

Even if one cannot decrypt the Riverbanks Ripper cryptogram, one can speculate about the content of the cleartext. Several forensic psychologists believe that the Riverbanks Ripper has encrypted his own name. If this is the case, solving the cryptogram might reveal the identity of one of the most-wanted criminals of the USA.

Can you solve the Riverbanks Ripper cryptogram? It’s certainly a tough one, but I know that my readers are very good at breaking even the most difficult encryptions.

Further reading: The Henry Debosnys Murder Case FAQ

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Kommentare (21)

  1. #1 Marc
    1. April 2017

    WOW, this one is really strange, the index of coincidence is : 100%

  2. #2 Largo
    1. April 2017

    This is one of the most curious cryptograms I’ve ever seen. I am almost sure that it is not only a substitution cipher. There must be some kind of transposition too! But where to start?

  3. #3 TWO
    1. April 2017

    Took a while but here is the solution :


    I used Ron Rivest’s asynchronacy theory and Marylin Monsan’s superscalar shifting paradigm analysis.



  4. #4 Kriston
    2. April 2017

    .…and Mr Cooper again.

  5. #5 Knox
    2. April 2017

    skyjacker 1971

  6. #6 Thomas
    2. April 2017

    Perhaps the rest is written with invisible ink, f.e. lemon juice which can be made visible with heat. Light a candle and hold the paper in the flame.

  7. #7 Klaus Schmeh
    2. April 2017

    I’m afraid, your solution is wrong. Ron Rivest’s asynchronacy theory and Marylin Monsan’s superscalar shifting paradigm are not applicable here, because the Hemming weight of the ciphertext normal form is too sesquilinear for a Laplace method to be surjective.

  8. #8 Thomas
    2. April 2017

    There is a stunning similarity to the eleventh symbol in the Zodiac killers message http://scienceblogs.de/klausis-krypto-kolumne/2014/07/10/die-sieben-bedeutendsten-zodiac-killer-trittbrettfahrer/.
    Maybe we can kill two birds with one stone …

  9. #9 Joseph Kuhn
    2. April 2017

    Modern cryptopsychoanalysis says, “I” means “I”. The killer sees himself as the one and only, illustrated by the classical phallic symbol.

  10. #10 Klaus Schmeh
    2. April 2017

    >There is a stunning similarity to the eleventh symbol
    >in the Zodiac killers message
    You’re right! This can’t be a coincidence.

  11. #11 Svechak
    2. April 2017

    There must be a link to the Bible: an “I” for an “I”.

  12. #12 tomtoo
    2. April 2017

    Iam not shure if i should start at the begin or the end ?

  13. #13 Nick Pelling
    2. April 2017

    I don’t want to worry you, but there are already three theory videos on YouTube about this, along with a self-published book by L.A.Braun explaining how Leonardo da Vinci made it.

  14. #14 Klaus Schmeh
    2. April 2017

    @Nick Pelling:
    >I don’t want to worry you, but there are already three
    >theory videos on YouTube about this
    Thanks for the hint. These videos are very interesting.

  15. #15 Ralf Bülow
    3. April 2017

    I am a very late thinker but then I heard the bell ringing, see more on Wikipedia: https://en.wikipedia.org/wiki/Riverbank_Laboratories

  16. #16 robsn
    3. April 2017

    Please excuse, but here is a question from a total layman who reads this blog just out of curiosity and usually does not comment.

    Why does anyone think that this is an encrypted message? It’s just a line! How did anyone come to the conclusion, that there is a hidden message in a single character? Would the same attention have been payed to an “X” or something?

    I read the text twice, but I don’t get it at all.

  17. #17 tomtoo
    3. April 2017


    You should look on the date Klaus has written this blogpost. ; )

  18. #18 robsn
    4. April 2017

    …woooaaaaa…… Thanks @tomtoo.

    Danke Klaus – wenigstens einer hat mich in den April geschickt. 😉

  19. #19 Nils Kopal
    4. April 2017

    Since it is only a single letter, I assume this is a Caesar cipher. Performing a Caesar cipher with only one letter, you get a perfect cipher. The probability for plaintext, key, and ciphertext are each 1/26. Thus, this message is unsolvable…

    Besides that, if it is not a Caesar cipher, I assume the message is not encrypted at all. The ripper just wrote a plea of guilty telling us that he (“I” am the killer) is the killer… :-)

  20. #20 Marc
    4. April 2017

    Stellt sich nur die Frage, was jetzt der “echte” Platz 39 ist oder war.

  21. #21 tomtoo
    5. April 2017

    @ Marc
    Evtl. die 14 ?