2The Case Serial killer active in the San Francisco area 1967 – 1974 (at least)Linked to 7 murders, but claimed many moreNever caughtPolice investigation closed in 2004Lots of theories and speculations around the case
3This is the Zodiac speaking... Wrote many letters (at least 18) to the police and to newspapers in the SF area
4Ciphers Four letters contained ciphers Appear to be substitution ciphers, but with more cipher text symbols than ordinary lettersTwo of them contain too little cipher text to be solved
5408 Cipher First cipher the Zodiac sent Was divided in three parts and sent to threedifferent newspapersAll three parts published on the front pagesSolved in a week by a high school teacher and his wife
6How Did They Do It?Knew the killer had a big ego, assumed he would start with ’I’Assumed the word ’kill’ would appear several timesThis was 1969 – only pencil and paper!Donald Harden
8Caesar CiphersMethod used by Romans for hiding messages; called “Caesar Ciphers”An easy way to hide messages is to shift each letter of the alphabet forward or backward a number of spaces.Let’s shift the alphabet backward by three and code the following message:FORENSIC SCIENCE USES CRYPTOGRAPHY TO SOLVE CRIMES.
10Caesar Ciphers Answer 3: Do number four! Answer 4: ZKBD YP DRO JYNSKM MYNO RKC LOOX LBYUOXThe Zodiac killer is still at large.
11This is quite cumbersome so let’s look at letter frequencies to speed this up. Most commonly used letters in descending order of frequency:E-T-A-O-N-R-I-S-H-D-L-F-C-U-M-G-P-Y-W-B-V-K-X-J-Q-ZDo number 5!Answer 5:The Zodiac killer uses complex ciphers.HVS NCRWOQ YWZZSF IGSG QCADZSL QWDVSFG
12Substitution CiphersIt would have been simple to break the code if the Zodiac killer had used a Ceasar cipher, but he didn’t.He used a substitution cipher. In a substitution cipher, either the alphabet is not in order or each letter of the alphabet is represented by a symbol.Do number 6!Answer 6:Donald Harden solved a zodiac cipher.