BIRMINGHAM, Ala. (AP) — Thomas Edwin Blanton Jr., the last of three one-time Ku Klux Klansmen convicted in a 1963 Alabama church bombing that killed four Black girls and was the deadliest single attack of the civil rights movement, died Friday in prison, officials said.

In May 2001, Blanton was convicted of murder and sentenced to life in prison for the bombing of the 16th Street Baptist Church in Birmingham.

Sen. Doug Jones, who prosecuted Blanton, said the fact that Blanton remained free for almost 40 years after the bombing “speaks to a broader systemic failure to hold him and his accomplices accountable.”

The church bombing, exposing the depths of hatred by white supremacists as Birmingham integrated its public schools, was a tipping point of the civil rights movement.

A 1993 meeting in Birmingham between FBI officials and Black ministers led to the reopening of the bombing case against Blanton and Cherry.