By Dan Merica, CNN

Washington (CNN) – Eleven years after the World Trade Center attack, the billion dollar memorial and museum dedicated to the victims of 9/11 is just half that - a memorial without an operating museum.

And though a dispute between New York City’s mayor and New York’s governor is responsible for delaying the opening, a separate legal battle is aimed at blocking one museum exhibit in particular: a large cross made of one of the twin tower’s T-beams that became a national symbol in the days after the 2001 attacks.

A national group called American Atheists is suing the museum to stop the display of the cross, arguing that a religious symbol has no place in a memorial that’s backed by public funds and that is supposed to serve as a monument to victims of many different religions - and to those who had no religion at all.

“It is important that it not be displayed to the exclusion of everyone else,” said David Silverman, president of the American Atheists, which first filed suit in July 2011. “This case is about inclusion, it is not about the elimination of religion, it is about the inclusion of everyone.”

The National September 11 Memorial & Museum says it included the cross because it “became an icon of hope and comfort throughout the recovery in the wake of the September 11, 2001, attacks.”

The case has gained national attention and has become important to many atheists and religious Americans alike. While atheist blogs and publications have pushed this case, spearheaded by American Atheists, conservative religious groups such as the American Center for Law and Justice have cited it as an example of growing anti-Christian sentiment and have filed an amicus brief in support of his display.

In light of all the attention, one legal expert says the atheists’ legal case is “absurd.”

“I think the odds of a court ordering the cross removed are literally zero,” said Jeffrey Toobin, CNN’s legal analyst. “The museum is not building a place for religious worship, they are preserving a historical relic that was meaningful to a great many people and part of the story of 9/11.”

Toobin compared the cross’s inclusion in the museum with the many other instances in which government-funded museums feature religious artwork.

“When the government is surveying a historic development, the government does not have to exclude religions images and artifacts from its displays,” Toobin said.

The 17-foot cross was discovered by Frank Silecchia, a construction worker who helped with the clean up and recovery at ground zero. The cross is a steel T-beam, a common architectural device used in the building of the World Trade Center towers.

The case hasn’t gotten anywhere since it was filed in U.S. District Court in Manhattan. The lawsuit names prominent government officials, including New York Mayor Michael Bloomberg and New Jersey Gov. Chris Christie, both of whom play a role in the deciding how the World Trade Center site is used.

Caught in a funding battle between Bloomberg on the one hand and Christie and New York Gov. Andrew Cuomo on the other, it is unclear about when the museum will open. The memorial opened last year, on September 12, after families of those killed on September 11 marked the 10-year anniversary at the memorial.

The museum did not respond to a request for comment.

In documents submitted to the court, the museum defends the inclusion of the cross, saying that “the 9/11 Museum is an independent nonprofit corporation. Its curators’ decisions to display particular objects, such as the Artifact, in the Museum are not state actions to which Constitutional protections apply.”

In the same documents, the museum argues that even if constitutional protections apply, “there is no legal authority for the proposition that a museum is prohibited from displaying an item with historical, cultural or artistic significance merely because that item also has religious significance.”

Silverman rejects that argument. “The argument that this is not a religious symbol is asinine and arrogant,” he says. “They want 9/11 to appear to be an attack on Christianity, and it was not.”

Shortly after plans for a 9/11 museum started to be worked out, Silecchia, the construction worker, and the Rev. Brian Jordan, a priest who ministered to firefighters and emergency responders at ground zero, began to press to the inclusion of the World Trade Center cross in the memorial and museum.

“First of all, it is an artifact of ground zero,” Jordan told the Irish Echo, a small publication in New York, in 2002. “And secondly, it is sacred ground, for God’s sake.”

Jordan declined interview requests, saying in an e-mail that “after a careful period of reflection, I have decided not to make any public comment at this time.”

In the same interview, Jordan argued that the reason it should be included is because most of the victims were Christians - “the plurality of which were Catholic,” Jordan said. The cross was first displayed near the edge of ground zero, until on October 5, 2006, the cross was moved to St. John’s Church, where it sat on the corner of Barclay and Vesey streets.

Jordan’s efforts for the cross’ inclusion were successful, when on July 23, 2011, Jordan blessed the cross at a ceremony in Zuccotti Park before it was transported into its permanent setting in the museum.

“After a 10-year journey of faith, the World Trade Center Cross has finally found its home,” Jordan said in a statement at the time.