Ah, Gareth, you got caught by a variation of the same misconception I had. I thought the quote was from Dietrich Bonhöffer, who was executed in a concentration camp in 1945 as a consequence of his involvement in the 1944 plot to assassinate Hitler. It's not - it's from Martin Niemöller (1892-1984). Niemöller also spent time in a concentration camp for his opposition to Hitler. Another source said the quote came from an address he gave to the U.S. Congress in 1968.
Here's the song by Christy Moore that Roger linked to. It's usually better to post lyrics of songs that we don't have here, along with a link to the source where you found them.

Yellow Triangle
(Christy Moore)

CHORUS
      

      Am       F            Am
        Black triangle, pink triangle
                 F            Am
        Green triangle, red triangle
                 F             Am
        Blue triangle, lilac triangle
                 F  G             Am
        And they wore the yellow triangle         

      

                  C            G                 Am
     When first they came for the criminals I did not speak
     F          C                 G
     Then they began to take the Jews
     F                     C               G                Am
     When the fetched the people who were members of trade unions
     F-G        Am
     I did not speak
               C               G        C                G
     When they took the Bible students, rounded up the homosexuals
                F               G                 Am
     Then they gathered up the immigrants and the gypsies
     Am
     I did not speak, I did not speak
           F          C       E7                F      G       Am 
     Eventually they came for me and there was no one left to speak
     
     CHORUS