Mismanagement of the Mississippi River Gulf Outlet may have exacerbated extreme flooding during Hurricane Katrina, but—contrary to two previous rulings—the U.S. Army Corps of Engineers can’t be held liable, according to a recent appellate court ruling.

The decision, handed down September 25 by the same U.S. Fifth Circuit Court of Appeals panel that in March said the Corps should pay, came as a shock to plaintiffs.

“[The decision] is devastating,” Joseph Bruno, a lawyer in New Orleans who represents the plaintiffs, told the New York Times. “I’m just amazed that the same three-judge panel that affirmed did an abrupt about-face and gave the corps a pass.”

Homeowners along the 76-mile MRGO shipping channel (called Mister Go) have long claimed Army Corps negligence in its design. Constructing the channel destroyed protective wetlands and the channel acted like a “hurricane highway," allowing Katrina’s storm surge to reach New Orleans, according to the Associated Press.

In 2009, U.S. District Court Judge Stanwood R. Duval, Jr., ruled that a law protecting the government from lawsuits for the failure of flood control measures did not apply to the MRGO because it is a navigation channel. He also rejected Army Corps arguments that maintenance decisions were “discretionary policy judgments of … professional staff and thus protected under federal law,” according to a March 2009 Times-Picayune article.

"Ignoring safety and poor engineering are not policy, and clearly the Corps engaged in such activities," Duval is quoted as saying.

But in September, the three-judge panel reversed Stanwood and its own March 2012 ruling by saying that the Corps’ misjudgments in not strengthening MRGO levees were policy decisions and that the Corps is therefore immune from liability.

“The corps's actual reasons for the delay [in armoring levees] are varied and sometimes unknown, but there can be little dispute that the decisions here were susceptible to policy consideration,” the September ruling states.

The panel might have reversed itself to avoid setting a precedent that would allow the Corps to be sued for future flooding, Mark Davis, a Tulane University law professor speculated in the Times-Picayune. The cost in this case alone could also be a factor. An Army fiscal report estimated in 2009 that damages could be as much as $500 billion in future claims, according to another New York Times article. Approximately 80,000 people live in the affected area, which includes St. Bernard Parish and the Lower Ninth Ward, the article stated.

The plaintiffs can have the Fifth Circuit hear the case again or take their appeal to the U.S. Supreme Court. Bruno didn’t say what action they would take, but that they would continue to fight. Another lead attorney in the case, Pierce O'Donnell, didn’t discount the enormous effort required to keep taking on the federal government. “It's a Herculean task,” he told the Associated Press. “The government makes the laws— they created the immunity; it prints the money—they have unlimited funds; and the case is tried in a building called the U.S. courthouse.”