It may be important to for him to use the Society's own publications as witness against itself. Even the Bible.
For example, the Proclaimers book on page 133 has a footnote near a sentence that says that the bible students believed that Christ's presence began in 1874. The footnote says, in part, "A clearer understanding of Biblical chronology was published in 1943, in the book “The Truth Shall Make You Free,” and it was then refined the following year in the book “The Kingdom Is at Hand,” as well as in later publications." That makes one think that the understanding of 1914 as the beginning of Christ's presence didn't come out until 1943. Very contrary to popular thinking that they always understood 1914 this way.
This is backed up by the book "God's Kingdom Has Approached!". In chapter 11, pages 209-210, paragraph 55, it says this, very pointedly:
"In the year 1943 the Watch Tower Bible and Tract Society published the book “The Truth Shall Make You Free.” In its chapter 11, entitled “The Count of Time,” it did away with the insertion of 100 years into the period of the Judges and went according to the oldest and most authentic reading of Acts 13:20, and accepted the spelled-out numbers of the Hebrew Scriptures. This moved forward the end of six thousand years of man’s existence into the decade of the 1970’s. Naturally this did away with the year 1874 C.E. as the date of return of the Lord Jesus Christ and the beginning of his invisible presence or parousia."
So, the understanding of 1914 did not come about until 1943.
The Bible, on the other hand, has a footnote on Hebrews 5:9 (using the old NWT Reference version) on the phrase "had been made perfect". The footnote reads: "Or, “after he had been inaugurated (installed; empowered; consecrated to office).” Gr., te·lei·o·theis′. See Le 21:10 ftn. Compare Le 8:33 ftn." The NWT, the JW Bible itself, admits Christ was inaugurated to office long, long before 1914.
These are the things that helped open my eyes a bit to the false teachings of JWs.