A Higher Form of Killing?

The book A Higher Form of Killing: The Secret History of Chemical and Biological Warfare by Harris and Paxman is still one of the best selling popular books on chemical and biological warfare.  Originally published in 1982, with a second edition published in 2002, the book's title is supposedly derived from a quote of Frtiz Haber, the Jewish-German chemist whom many regard as the father of chemical warfare.  

In no future war will the military be able to ignore poison gas. It is a higher form of killing.
— Fritz Haber quoted in Harris and Paxman, 1982

Almost all other books on chemical warfare written since 1982 use this quote, and all of those that that do cite Harris and Paxman as their source.  Harris and Paxman attribute the quote to Haber's 1919 Nobel Prize acceptance speech without further citation. (Haber was awarded the 1918 Nobel Prize for chemistry for the synthesis of ammonia from its elements in November of 1919 and his acceptance speech was in 1920, not 1919 as Harris and Paxman cite). Haber never said that in this acceptance speech.  See for yourself.

In the 2002 edition of A Higher Form of Killing, the attribution of the quote was changed to Haber, 1923, without any further attribution or citation. I found that rather curious and thus I sought to find its source as it is a great quote for those of us who study the history of industrial gases and chemical warfare.   I  traced every use of the quote in print and on the internet back to Harris and Paxman, I read everything Haber wrote/said in english between 1919 and 1923, and I returned to Stoltzenberg's 2004 Biography of Haber, considered the best recent biography of Haber.  I even scoured the finding aids of the Fritz Haber Papers (with the help of google translate) at the Leo Baeck Institute, Center for Jewish History, yet all of my searches proved fruitless.  Thus, after extensive research I have come to the conclusion that Fritz Haber never uttered those words.  I would love to be proven wrong.