Don Cameron's book "Captive to a Concept" was the nail in the coffin for me. It is an astounding book highlighting the trap JW's are in. "Crisis of Conscience" for sure also helped but Don's book just tipped it for me after I researched as a PIMI elder about the destruction of Jerusalem.
I was challenged by a minister on the doors that 607 BCE was made up by the JW's so I spent 6 months researching it...which left me lurking on here...Cedars website etc and then Don's book was it and I resigned as an elder and a few months later faded never to go back.