Updated at 6:02 p.m. ET: TACOMA, Wash. -- Hundreds of mourners gathered at a church Saturday to remember "two beautiful boys" killed when their father burned their house to the ground with himself and his sons inside.

Sunday's murder-suicide arson, which claimed the lives of Josh Powell and his sons, Charles, 7, and Braden, 5, capped a grim family saga that began more than two years ago with the disappearance of the boys' mother, Susan Powell, under suspicious circumstances in Utah.

The two brothers were at the center of a bitter custody dispute between their father and the parents of his missing wife. Investigators now presume Susan Powell was slain by her husband, though her body has yet to be recovered.

"This moment is about two beautiful boys," Pastor Dean Curry, lead pastor of the Life Center church in Tacoma, an Assemblies of God congregation, said to open Saturday's service.

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Braden and Charles Powell

"There have been all kinds of things said surrounding those boys," Curry added. "But what we do here, and the spirit that we do have here, is up to us."

The boys’ grandparents, Chuck and Judy Cox, briefly took the platform to thank law enforcement and others in the community who offered their support "through this trial that we’ve endured."

"Everyone was doing everything they possibly could to keep them safe," Chuck Cox said.

Teachers also shared memories of the boys.

Charlie Powell’s kindergarten teacher, Tammy Ougheon, remembered the 7-year-old as "an amazing young man" with an appreciation of nature who loved to collect bugs, rocks and plants. "He is safe in his mother's arms," she said.

His younger brother, Braden, preferred cars and trains, teachers remembered, and last Halloween got to dress up as a Transformer. Braden, teachers said, loved to be tickled.

"His little spirit lives on in the hearts of all who knew him," said Kristie King, an instructor at a YMCA that Braden attended.

Many of the mourners wore purple and blue ribbons in memory of the children.

At the front of the church's sanctuary, the boys were in a single casket topped with a large flower arrangement that included daisies, roses and sunflowers. Three screens in the sanctuary showed a photo of Susan Powell and the two boys, all smiling.

Ted S. Warren / Pool via Getty Images

Chuck Cox reaches out to touch the casket bearing his grandsons, Charlie Powell and Braden Powell, as he walks with his wife Judy Cox during Saturday's funeral service.

At the family's request, members of the public were invited to attend the memorial. Curry said earlier he expected as many as 2,400 people to turn out for the service.

A private family interment will take place Monday at Woodbine Cemetery in Puyallup.

Pierce County sheriff's spokesman Ed Troyer said Saturday that Josh Powell's body will be released to a cousin Monday.

Last week, a judge denied Josh Powell's bid to regain custody of his sons, citing the "extreme child porn" found last September in the house he rented near Tacoma.

That discovery had led to the arrest of the boys' grandfather, Steven Powell, who had been living with them and whose vast pornography collection included images of their missing mother. He now awaits trial on criminal charges related to the photos.

The boys were ordered on Feb. 1 to remain in the custody of their maternal grandparents, Charles and Judy Cox, at least until Josh Powell, 36, submitted to a psycho-sexual evaluation.

In this bank surveillance photo released by the Pierce Co. Sheriff's Dept., Josh Powell, left, is seen making a withdrawal at a bank in Puyallup, Wash., on the day before Powell and his two young sons were killed.

Four days after that decision, a child welfare case worker delivered the two boys to their father's home for what was supposed to be a supervised visit. But he abruptly locked her out, then set off a fiery explosion that consumed the house as the worker, herself uninjured, watched in horror and called authorities by phone.

Medical examiners later said the two brothers had suffered chop wounds from hatchet blows inflicted by their father moments before all three died from smoke inhalation.

911 operator in Powell case: 'It was horrible'

Pierce County prosecutor Mark Lindquist said earlier this week that he considered "the murder of those children a confession to the murder of Susan Powell" and that he viewed the ongoing investigation into her fate as a murder investigation.

At the time his wife was reported missing, Josh Powell told police he had taken his sons camping in subfreezing temperatures just after midnight on Dec. 7, leaving his wife at home, and that she had vanished by the time they returned that afternoon, according to court documents.

The grandfather, Steven Powell, 62, was charged in September with 14 counts of voyeurism and one second-degree charge of possession of child pornography. Shortly after that, the boys were placed in the custody of their maternal grandparents.

The Associated Press and Reuters contributed to this report.

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Updated at 4:40 p.m. ET: Bobby D, the host of the Seattle radio show where Westboro Baptist Church founder Fred Phelps Jr. spoke, writes on the show's site that he offered Phelps the opportunity because "it's about the family":

You think I WANT to have these people on a show that I have worked so hard at perfecting to my liking?  NO way.  Having said that, I care about people and I DO NOT want them at a place that needs to be peaceful and a time ONLY for grieving and remembering.

Original post: Westboro Baptist Church, the virulently anti-gay group known for protesting at military funerals, has canceled its plans to protest the funeral Saturday of the two young boys who were killed last weekend by their father, Josh Powell.

The church, which is based in Topeka, Kan., had asserted that the deaths of Charlie and Braden Powell were payback from God over the Washington Legislature's recent endorsement of same-sex marriage.

A radio talk show offered the church time to express its views if it agreed to call off the protest. After Fred Phelps Jr., founder of the church, was interviewed on the program, he tweeted that the protest had been called off. 

(Phelps used the wrong Twitter handle for the show in his tweet, leading msnbc.com to misidentify the show he had appeared on. It was the Bobby D Show based in Seattle and Tacoma, not the show of the same name by a different host in Belleview, Fla.)

More than 1,800 people had sounded off on Facebook pledging to join Occupy Seattle in showing up at a counterprotest at Life Center Church in Tacoma, south of Seattle. 

The Powell family asked anyone who didn't intend to celebrate the boys' lives to stay away from the service Saturday morning, which NBC station KING-TV reported will be open to the public. The church plans to live-stream the service.

Police also ask people not attending the service to stay home. 

Cops: Powell computer depicted parent-child sex

Charlie, 7, and Braden, 5, died Sunday when their father, Josh Powell, set fire to his home in Graham, near Tacoma. Authorities said Powell, who was already under investigation in the disappearance of his wife in Utah two years ago, attacked his sons with an ax before all three died in the fire and explosion.

Westboro has protested at military funerals and public schools across the country to advance its contention that God hates homosexuality and is punishing the U.S. because of it. It takes an over-the-top confrontational approach to opponents and the media, ensuring that it generates attention wherever it shows up. 

Friday, Phelps' daughter, Margie, tweeted after the announced cancellation that she was looking forward to counterprotesters' showing up at the funeral even though the protest had been canceled:

"imagine noisy mob Sat.raging in vain! Chuckle."

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Nightly News

Josh Powell and his sons.

SEATTLE -- A computer in Josh Powell's former home in Utah had animated images that depicted "incestuous" sex between parent and child, Pierce County authorities said, and a state official said the material prompted a judge to order Powell to undergo a psycho-sexual evaluation just days before he killed his children and himself.

Pierce County Sheriff's Detective Ed Troyer told The Associated Press on Thursday night that the images collected by investigators in Utah two years ago were realistic computer-generated depictions of "incestuous" parent-child relations.

The documents and images were recovered by police in West Valley, Utah, and sent to the Pierce County Sheriff's Department under a restrictive court order on Feb. 1, NBC station KING 5 reported. According to Washington's Department of Social and Health Services Public Affairs Senior Director Thomas Shapley, the material prompted the court to stop a process that likely would have returned Charlie, 7, and Braden, 5, to their father's custody.

Shapley said the material found on the computer was so disturbing that it prompted the state psychologist consulting in the custody case to change his opinion and recommend that the court prevent the return of the children.

An attorney for Powell's in-laws wasn't invited to see the materials before a custody hearing last week, the AP said. Lawyer Steve Downing told the AP that he might have asked the court to change the terms of Powell's supervised visitation with the boys -- if he had seen the images.

Meanwhile, the state social worker who brought Powell's two boys to his house said she heard the father tell one son he had a "surprise” for him, according to ABC News.

Elizabeth Griffin-Hall said in an interview to air on ABC's "20/20" on Friday that Powell slammed the door on her after he had the children inside the house on Sunday. Hall said she knocked on the door to try to get inside and heard Powell tell 7-year-old Charlie: "I've got a big surprise for you."

She also heard 5-year-old Braden cry out, but she said she thought the child had hurt his foot.

“The door slammed in my face,” Griffin-Hall said.

“I saw Josh for just one second, his eyes caught mine. He had a look in his eyes. If I were to describe it, it was friendly enough. It was just kind of sheepish. He shrugged his shoulders up."

Authorities said Powell used a hatchet on his children, then set a house fire that killed them all.

Powell's wife, Susan, vanished in Utah two years ago. Josh Powell had been a person of interest in the case but maintained that he had taken his boys — then 2 and 4 — on a midnight camping trip in freezing temperatures when she disappeared from their home.

Anti-gay church to protest at slain Powell boys’ funeral

Griffin-Hall said Charlie and Braden loved being with their father.

She described Powell as a devoted dad, who always had surprises for his boys.  

"One of them said what he wanted to do was go home and live with his daddy," she told ABC, adding that the boys would "light up" during visits with Josh Powell.

'I did everything'
After he got the boys inside and locked the door, Griffin-Hall said she kept banging on the door and asked Josh Powell if she could help him or the boys. She said she realized she didn't have her phone and walked back to her car, which was 10 steps away.

She then called 911 and her supervisor to tell them what was going on. The 911 dispatcher's handling of that call has been criticized, and an investigation has been launched into the emergency response.

The social worker said she told her boss "something terrible is happening here, and I was on the phone with ... when the house exploded."

"I wanted to get to the kids," she said. "I wanted to get to the kids. I would have broken in if I could."

But Griffin-Hall told ABC she doesn't think she could have saved them.

"How this happened is that Josh Powell was really, really evil. I couldn't have stopped him," she said. "I did everything I was supposed to do. I did everything right and the boys are still dead."

This post contains reporting from NBC News, The Associated Press and msnbc.com staff.

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