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.