On April 30, 1967, exactly six months after the murder of Cheri Jo Bates, three nearly identical letters were sent to the victim's father Joseph Bates, the police, and the Press Enterprise in Riverside.
The letters were written on lined notepaper.
The unsigned letter to Cheri Jo Bates' father, read:
SHE HAD
TO DIE
THERE WILL
BE MORE
The other two letters addressed to the Police and Press Enterprise read:
BATES HAD
TO DIE
THERE WILL
BE MORE
Source: Wikisource.org
These messages were signed with a letter or symbol that resembled the letter Z with a curved top.
The letter envelopes carried two four-cent stamps each, which was more postage than necessary.
It has been widely assumed that the letters had been authored by the same individual that wrote the Desktop Poem and the Confession Letter.
If the letters had been authored by the Zodiac Killer is still debated.
Source: Wikisource.org
For the following reasons, we believe that actually both has been the case.