On the morning of September 15, 1963, Rev. John H. Cross Jr. and members of the 16th Street Baptist Church in Birmingham, Alabama, were preparing to start the Youth Day worship service when a bomb went off.

"I will never forget that horrific noise," said Barbara Cross, the reverend's eldest daughter. "I remember everything got real dark and you could hear kids screaming."

At 10:22 a.m. a massive explosion sent glass, cement and debris flying. An FBI investigation later discovered that four Ku Klux Klan members (KKK) had planted dynamite under a cement staircase outside of the church.

The blast knocked down power lines and blew a hole in the side of the building, completely destroying the ladies restroom in the basement where a group of girls had been getting ready for church.

Four little girls were killed in the church that Sunday morning: 11-year-old Denise McNair, along with 14-year-olds Cynthia Wesley, Carole Robertson and Addie Mae Collins. Nearly two dozen others were injured.

In the 60 years since the 16th Street Baptist Church bombing, the church has been rebuilt, and stained glass has been repaired, but there are still wounds time has yet to heal. Family and friends say decades later they are still holding on to their memories and grieving the loss of the four girls who were killed that day.

Addie Mae Collins

Her sister was the 5th girl in the restroom

The four girls who died weren't alone in the basement that bloody Sunday. Addie Mae's sister, 12-year-old Sarah, was also caught in the explosion.

Decades later, Sarah Collins Rudolph told CNN she remembers Denise asking Addie Mae to tie the sash on her dress. But before her sister could tie the bow, the bomb went off, she said.

The force of the blast hurled pieces of glass and shrapnel that were embedded in Collins Rudolph's face. The blast not only stole her big sister's life -- and the lives of her friends -- but it also took Collins Rudolph's eyesight.

"When they took the bandages off my left eye, at that time, I couldn't see nothing but a little light," she recalled. "That right eye, it was messed up so bad, so they just had to remove it."

Collins Rudolph has spent the rest of her life with a prosthetic eye.

"When they put that bomb under that church, they didn't know who they were going to kill. They didn't care," she said.

Addie Mae was a quiet girl and always walked to church with her sisters, Sharon Owens, a childhood friend of the four victims, recalled. "They were just the sweetest," she said.

Whenever she outgrew her clothes, Owens said her mother would always say, "We gotta remember the Collins girls." And so, they developed a routine of passing down her clothes.

Decades later, Owens said many in the Birmingham community are still traumatized from the bombing.

History recognizes "those that did not make it, but they don't recognize those that went through the horror," she said.

Collins Rudolph said she is still facing continuous health complications since the bombing and still paying out-of-pocket for her medical bills. She said she would like restitution from the state of Alabama for her suffering.

"It's been so long, I need that apology," she said. "They took my whole life away from me."

Denise McNair

Girl talks and Beverly Hillbillies

Denise, often called 'Niecy' by her friends, was the youngest victim of the church bombing. Rhonda Nunn, Denise's neighbor and childhood friend, remembers her as a compassionate and loving girl.

She said she will never forget the day Denise walked to her house holding a lifeless bird after one of Birmingham's notorious summer storms.

"I'm like, 'Oh, you should put that down,'" she recalled.

Instead, Denise insisted that they host a funeral, and with help from the other neighborhood kids, they placed the bird in a large matchbox to bury it.

Maxine McNair, Denise's mother, came across the street and sang "one of the most beautiful versions of the Lord's prayer I have ever heard in my life," Nunn recalled.

"I have never been to a funeral more precious than that one."

While Nunn worked in her flower garden, she and Denise would write poems, make up stories and have girl talk.

"She was one of the few people that I felt comfortable talking to," Nunn said. But after the bombing, things weren't the same in the garden.

"For a while I wouldn't even go out there," she said. "I cried every time I went."

Nunn said Denise enjoyed watching Beverly Hillbillies with her younger sister, Barbara.

"And then after Niecy passed, my sister thought the best way to stay in touch was to keep her updated on what was going on Beverly Hillbillies," Nunn said. After a new episode, Barbara would retreat to the bathroom in the back of their home to tell Denise about the show, Nunn said.

Lisa McNair, Denise's sister, was born a year after she was killed and never had the chance to personally know her sister.

"My dad would tell me she was very precocious," McNair told CNN. "He said she was a real leader, very headstrong and driven."

"We'd often say if she lived, she probably would have been a lawyer because she was always making a point," McNair said. "I think in her death, she still is teaching lessons."

Carole Robertson

'She was a peacemaker'

Carole Robertson was the baby of her family, which consisted of her oldest brother, Alvin Robertson Jr., and her older sister, Dianne Robertson.

"We were a very close-knit family and did a lot of things together," Dianne Robertson told CNN.

"The thing that always amazes me was that she was the youngest child, but oftentimes showed much more wisdom than her age," she said.

And when tensions rose in the household, "she was always the mediator between me and my brother," Dianne recalled.

"She was a peacemaker."

Six decades later, Dianne said she still wonders what her sister would have grown up to be.

"She had so many positive characteristics and interests."

Carole was a straight-A student who loved reading and volunteering at the Smithfield Public Library, her sister said.

She was actively involved in Girl Scouts, the leadership organization Jack and Jill of America, as well as the Parker High School's science club and marching band. Their father, Alvin Robertson Sr., was a musician and he taught Carole how to play the clarinet, Dianne said.

Dianne moved away for college two years before her sister was killed.

"That's part of what I regret," she said. "I was away in college, and that's the time we could've started bonding even more."

Dianne said on the morning of the bombing, their "mom had allowed (Carole) to select a shoe that had a little 2-inch heel on it."

"It was her first shoe that wasn't flat and I know she was happy about that."

Dianne was in New York with her aunt when the bomb detonated.

"When she told me what happened, I fainted," she recalled. "It was unbelievable ... How in the world could something like this happen?"

Cynthia Wesley

'She was always laughing'

Cynthia was adopted into the Wesley family. Childhood friend Owens said she recalls attending vacation Bible school with Cynthia during the summer of 1962, and remembers her as a "social butterfly."

"She was a bit older, you know, but we looked up to the big girls," Owens said. "We would go to the bathroom at the church and they would be in there putting on their makeup and fixing their hair."

Carolyn Maull McKinstry, another childhood friend, said Cynthia was always happy and just a lot of fun to be around.

"She was always laughing," she said.

Maull McKinstry remembers Cynthia to be petite and said she often admired her outfits. "I would look at her and wonder, 'Where did she find these dresses that fit so neat and nicely?'" she said.

Cynthia's mother, Gertrude Wesley, made her clothes. "I learned that she was an educator, but she was also a seamstress," Maull McKinstry said. "And an excellent one."

The two childhood friends were also a part of the 'Cavalettes', a fellowship club for young girls. Dues were only a quarter, and the all-girls club would meet at each other's houses.

"It was always a happy time when all of us would get together," Maull McKinstry said. "We would just play records and dance."

On the day of the bombing, the club had a meeting scheduled at 3 p.m. "We were all excited," Maull McKinstry said.

She said she left the basement to go upstairs minutes before the bomb went off. Losing her friend and processing the bombing was something Maull McKinstry struggled with for a long time.

"I was 15 when the church was bombed -- but then I was 15 for the next 20 years."

'Bombingham' and the four Klansmen

"The death of those four girls was the largest loss of life at one time" during the civil rights movement, according to Barry McNealy, the historical content expert at the Birmingham Civil Rights Institute.

Bombings were so frequent in Birmingham the city was dubbed "Bombingham," according to McNealy.

The 16th Street Baptist Church was historically a place for civil rights activists to host strategy meetings.

"So the church was a natural target for someone who was trying to make a dramatic statement," McNealy said.

Two years after the church bombing, the FBI identified four Klansmen as the primary suspects: Thomas Blanton, Bobby Frank Cherry, Herman Frank Cash and Robert 'Dynamite Bob' Chambliss.

"Chambliss had been a leader in planting bombs since the 1930s in Birmingham," McNealy said. 

The investigation closed in 1968 without any charges filed due to witnesses being "reluctant to talk and physical evidence was lacking," according to the FBI.

In 1976, news that then Alabama Attorney General Bill Baxley had reopened the investigation into the bombing became public. The investigation ultimately led to the conviction of Chambliss in 1977. Decades later, Blanton was convicted and sentenced to four consecutive life terms in prison in 2001, CNN previously reported. Cherry's conviction followed in 2002.

Cash died in 1994 and was never charged in the case, CNN previously reported.   

'A love that forgives'

The four girls' families and loved ones continue to push on their legacy to make sure what happened on that bloody Sunday is never forgotten.

In her book "Dear Denise: Letters to the Sister I Never Knew," Lisa McNair wrote letters that she wishes she could share with her late sister.

Dianne Robertson went on to name her daughter after Carole. She also remains active at the Carole Robertson Center for Learning and in Jack and Jill of America, which honors her sister every year.

While the tragedy left a void and longlasting pain and anger, forgiveness was a common theme shared across the families and friends who spoke to CNN.

"My parents quickly helped us understand that all White people weren't evil and didn't want us to die," McNair said. "Some of them could love us and want to be our friends."

On the Sunday of the bombing, Rev. Cross had planned to deliver a sermon called 'A love that forgives.'

Although the church was bombed before the message was preached, the lesson still rings loud and clear.

"I used to say this saying, 'May men learn to replace bitterness and violence with love, love, love, love," his daughter, Barbara Cross said. "I said it four times in memory of each girl."