The dispute over the design, which started after the winning entry was announced in 2005, was reignited by Burnett last month, before the sixth anniversary of the terrorist attacks.
But even so, plans are quietly taking shape for a grand tribute to honor the 40 men and women who lost their lives in what, many believe, was the first battle in the war on terror.
Since its designation by Congress in 2002, the park in southwestern Pennsylvania's Laurel Highlands has been troubled by slow fund-raising, threats to its federal funding, environmental hazards, and difficulty buying the land.
Still, supporters are confident the park will open on Sept. 11, 2011, the 10th anniversary of the attack.
When done, the memorial will hold a unique place in National Park Service history.
"There has never been a National Park Service area designed through an international competition as an entire unit before," said John Reynolds, chairman of the Flight 93 Advisory Commission and a former regional park service director.
Scarred by decades of coal mining, the landscape has a stark beauty that shifts with the high-altitude weather.
Here the forest was stripped, leaving a barren field and acid ponds of mine waste. The most prominent landmark, a huge rusted drag line, towers over the site.
To Murdoch, a Los Angeles architect whose proposal for the park was selected from more than 1,000 entries, the raw, industrial landscape - disfigured again by the terrorist attack - is integral to the story.
"The violation to the land is part of its history," said Murdoch, while giving a reporter in July the first media tour of the site. "The character of the land is integral to the experience of the memorial park."
Murdoch sees his approach, with its massive use of native trees and plants, as a path toward healing the land and, with it, the spirit of a wounded nation.
His plan encompasses 1,300 acres of the park (the remaining 900 acres will be a buffer zone to prevent development). It features elements rich with symbolism and crafted to blend with nature.
A carillon, 93 feet high, called the Tower of Voices will mark the entry. Its chimes will represent the voices of the passengers, whose gripping last words to loved ones captured the terror of their final minutes.
"Their last memory was voices on the phone," said Murdoch.
Two 40-foot-high walls - the altitude of the Boeing 757 just before impact - will open onto a viewing area of the "sacred ground," the final resting place of those on board.
A visitors' center will house artifacts collected at the site and exhibits on the attack.
"We wanted a design that would tell the story for succeeding generations about what happened that day, not just for those who lived through it," said Ed Root, who served on the final competition jury and whose cousin, Lorraine Bay, was a flight attendant on the plane.
"You can't tell the Shanksville story in a vacuum. You have to tie it in to what happened everywhere else, and do it in a setting that takes advantage of the landscape and beauty of the area."
Murdoch, 50, a Newtown Square native, counts as influences childhood trips to Philadelphia historic sites and the work of the city's renowned architect, Louis Kahn.
But his vision for the park was aided by a different memory: a family camping trip in the 1960s to the area.
"I remember the drama of the landscape," he said. "One of the things I remembered as a kid was color in autumn. Of course, the middle of September was the time of the [terrorist] event."
Until now, Murdoch has primarily designed public buildings that use unique features of their environment.
In considering his entry for the Flight 93 competition, he said he sought to bring intimacy to a large-scale landscape through a series of frames highlighting natural and historical features, such as the sky and the flight path.
But controversy erupted almost immediately upon his selection. Conservative columnists, talk-show hosts, bloggers and U.S. Rep. Tom Tancredo (R., Colo.) seized on what they perceived to be Islamic influence in the design, even sympathy for the terrorists - mainly, the crescent shape of the plantings, painted autumn red in drawings.
Since then, some critics have backed off, but Burnett wants an investigation.
"When we talked about the design, it was clear it was riddled with Islamic symbols," said Burnett, whose 38-year-old son helped lead the attack on the hijackers.
"My son Tom led that effort to take the plane back," he said, "and he should not have his name bastardized."
Murdoch takes a Zen-like approach to his critics, calmly pointing to the use of the crescent in many cultures and architectural styles. He said the memorial design is a reflection of the area's topography, the flight path, and the location of the impact site.
Murdoch said he tried to respond to the concerns by adding more trees to nearly complete the circle.
Reynolds said the park service consulted Islamic experts who saw no Islamic references in the design.
"I feel badly that [Burnett] has bought into the conspiracy theory," he said, "because none of it is true."
Joanne Hanley, the park's superintendent, said, "The NPS will build the memorial as designed."
But Burnett says unless the design is scrapped, he will withhold the use of his son's name, which historians say would leave an unacceptable hole in the story of Flight 93.
"Future citizens," said Reynolds, "have a right to know the names of those on the plane."
A long road lies ahead before any ribbons are cut here.
In all, 60 acres in the 1,000-acre heart of the park have been acquired, although officials say negotiations with major landholders are progressing, and fund-raising is $17 million shy of the $58 million needed.
Supporters remain firm in their belief that the park will open, even if incomplete, in four years.
After all, they say, these were the citizen heroes of 9/11. Since that heartbreaking day, hundreds of thousands of people have taken a 15-mile detour off the Pennsylvania Turnpike to pay them homage.
Many visitors leave something behind - a baseball cap, a flower, or small message. Because no official place exists to hold their thoughts, they write on whatever is available. The parking-lot guard rails are covered with their words: "We will never forget."
The unarmed passengers and crew - among them a retired special-ed teacher, an arborist, a software salesman and college students - defeated the hijackers' plot to use their plane as a missile to attack Washington.
"This was an act by 40 heroes, one of the most selfless acts in the history of the country, not a grand military campaign," Murdoch said, in describing his effort to build a memorial that is both bold and understated. "These were everyday people who did something extraordinary."
Contact staff writer Amy Worden at 717-783-2584 or email@example.com.