(CNN) The last convicted bomber in the 1963 Birmingham church bombing that killed four young African American girls has died in prison, nearly 60 years after the terror attack targeted the US civil rights movement.
Former Ku Klux Klan member Thomas Edwin Blanton Jr. was convicted in 2001 of murdering the four young African American girls killed after a powerful bomb exploded at the 16th Street Baptist Church on September 15, 1963.
The bomb collapsed a basement wall, killing Addie Mae Collins, Cynthia Wesley, Carole Robertson -- all 14 -- and Denise McNair, 11, in a lounge they used for changing into their choir robes.
Blanton -- one of three former KKK members convicted of murdering the girls -- died of natural causes Friday while serving a life sentence, according to a statement released by Alabama Gov. Kay Ivey.
"His role in the hateful act on September 15, 1963 stole the lives of four innocent girls and injured many others," Ivey said in a statement. "That was a dark day that will never be forgotten in both Alabama's history and that of our nation.
"Although his passing will never fully take away the pain or restore the loss of life, I pray on behalf of the loved ones of all involved that our entire state can continue taking steps forward to create a better Alabama for future generations," Ivey said. "Let us never forget that Sunday morning in September of 1963 and the four young ladies whose lives ended far too soon, but let us continue taking steps forward to heal, do better and honor those who sacrificed everything for Alabama and our nation to be a home of opportunity for all."
Blanton was 82 when he died after going into cardiac arrest Friday at William Donaldson Correctional Facility, according to the Jefferson County Coroner's Office.
"The preliminary autopsy results found no evidence of trauma or foul play, but did reveal the decedent had significant natural disease consistent with his known documented medical history," Chief Deputy Coroner Bill Yates said in a statement.
The Klan targeted the church because it was a leading African American institution and served as a staging area for the marches that met fierce resistance from Birmingham Public Safety Commissioner Bull Connor, brutality that has lived on in television footage and defines the city for many people to this day.
The Klan hoped the attacks would derail the movement as the marches had wrung concessions from local leaders and the state had begun integrating schools days before the bombing. But historians contend the church bombing marked a turning point in the civil rights movement and contributed to the passage of the Civil Rights Act of 1964.
President John F. Kennedy expressed hope in the aftermath of the bombing that it would spur action against racial hatred.
"If these cruel and tragic events can only awaken that city and state -- if they can only awaken this entire nation to a realization of the folly of racial injustice and hatred and violence -- then it is not too late for all concerned to unite in steps toward peaceful progress before more lives are lost," he said.
Fifty years after the attack, President Barack Obama awarded the four girls posthumous Congressional Gold Medals.
At the 2013 medal ceremony, House Speaker John Boehner recalled details of the girls' lives.
Addie Mae went door-to-door after school selling aprons and potholders her mother made. Denise put on skits in the garage to raise money for muscular dystrophy research.
Carole made sure her chores were done so she could go to dance class on Saturdays, while Cynthia excelled in math and band.
Victims' siblings remember on bombing anniversary
In a 2008 interview on NPR, Chris McNair remembered seeing his daughter's body on the day that shocked the nation.
"We drove over to a hospital, and we fumbled around, and we found somebody else who had been in the morgue," he told reporter Michele Norris. "And there lay all four of them, there side by side on the table. And Denise was lying out there with a piece of mortar, it looked like a rock, mashed in her head."
McNair's sister, Lisa, issued a statement after Blanton's death, obtained by CNN affiliate WBRC.
"I wished I could have sat down with him to find out if he had had a change of heart. But ultimately, I hope that he repented to the Lord for this sin and made his peace before he died," it quoted her as saying.
Alabama Sen. Doug Jones, who prosecuted Blanton as the US attorney for Alabama in 2001, posted on Twitter: "No matter what I do in my life, I will always be most proud of achieving justice for those 4 young girls. Blanton never atoned for his sins but his passing at this moment seems fitting. The journey to racial justice is long but I believe America is ready to finish it - together."
Blanton avoided justice for 38 years before his 2001 conviction, but not because the case was a bona fide mystery. Within days, the FBI suspected that Blanton and fellow KKK members Robert Edward Chambliss, Bobby Frank Cherry and Herman Frank Cash were responsible for the attack after civil rights protests and other bombings had rocked the city nicknamed "Bombingham."
Alabama Attorney General Bill Baxley convicted the then-73-year-old Chambliss in 1977, after reopening the case in 1971, and then the case remained dormant for decades. Chambliss died in prison in 1985.
Baxley contended that the FBI, which had informants in the Klan in the 1960s and wiretaps on Klan members, wouldn't share the information that would allow him to build a case against Blanton, Cherry and Cash.
In 1997, after other successful prosecutions for murders during the civil rights era, the FBI's Birmingham office reopened the case. Jones, the US attorney for the Northern District of Alabama during the Clinton administration, made it a personal crusade.
Cherry, who was convicted in 2002, died in prison in 2004. Cash, who died in 1994, was never charged in the case.
In 2016, Blanton asked the Alabama Board of Pardons and Paroles to let him die as a free man, but the panel denied his request, ruling he wouldn't be eligible again until 2021.