One-hundred years ago today, the state of Utah executed Joe Hill, silencing the union organizer and songwriter who gave us “There is Power in a Union” and “Casey Jones — the Union Scab.”

Born Joel Hägglund in 1879 to Swedish parents, Hill became a staple on picket lines and at worker rallies, belting out songs collected in the Industrial Workers of the World’s “Little Red Songbook.” In 1914, after a dubious trial, Hill was convicted of murdering a grocer and his son. An extensive exoneration campaign failed. Yet the three firing-squad bullets that ended Hill’s life cemented his status as a labor movement icon.

In the following letters — both sent during his imprisonment in Utah and excerpted from Haymarket Books’ newly released collection of his missives — Hill explains his motivation for writing union songs, urges labor to prioritize female workers, and briefly outlines his final wishes.