Solution claimed to Zodiac's last code

A hobbyist codebreaker believes he's cracked the Zodiac killer's last encoded message (above). It is, he claims, a Caesar cipher with some substitution stuff, though it's not really clear from the article. His solution identifies Arthur Leigh Allen as the killer:

KILLSLFDRHELPMEKI
LLMYSELFGASCHAMBE
RAEIOURDAYSQUESTI
ONSABLEEVERYYWAKI
NGMOMENTIMALIVEMY
PRIDELOSTICASTGOO
NLIVINGINTHISWAYK
ILLINGPEOPLEIHAVK
ILLDSOMANYPEOPLEC
ANTHELPMYSELFIMSO
ANGRYICOULDDOMYTH
INKIMALONEINTHISW
ORLDMYWHOLELIFEFU
LOLIESIMUNABLETOS
TOPBYTHETIMEYOUSO
LVETHISIWILLHAVKI
LLDELEVENPEOPLEPL
EASEHELPMESTOPKIL
LINGPEOPLEPLEASEM
YNAMEISLEIGHALLEN

With spaces, that reads "KILL SLF DR HELP ME KILL MYSELF GAS CHAMBER AEIOUR DAYS QUESTIONSABLE EVERYY WAKING MOMENT IM ALIVE MY PR IDE LOST I CAST GO ON LIVING IN THIS WAY KILLING PEOPLE I HAV KILLD SO MANY PEOPLE CANT HELP MYSELF IM SO AN GRY I COULD DO MY THINK IM ALONE IN THIS WORLD MY W HOLE LIFE FUL O LIES IM UNABLE TO STOP BY THE TIME YOU SOLVE THISI WILL HAV KILLD ELEVEN PEOPLE PLEASE HELP ME STOP KILLING PEOPLE PLEASE MY NAME IS LEIGH ALLEN".
I always assume "multiple keys used for different parts of the ciphertext", "bible codesque frequency shenanigans", etc., with these things. And it contains no new information, just the prime suspect and generic pathos. Cynical, I know! Be sure to drink your ovaltine.