The U.S. government spends tens of millions of dollars each year persuading federal circuit courts to uphold orders for thousands of illegal immigrants to leave the country, but those orders have been enforced in only one-fifth of the cases, according to sources familiar with a recent Justice Department study.

Immigration and Customs Enforcement, a branch of the Department of Homeland Security, is responsible for "removing" illegal immigrants who stay in this country against the law. But the study found that more than 80 percent of the illegal immigrants whose deportation orders were upheld by a federal appeals court last year were still in the country as of five weeks ago, according to an internal Justice Department memo obtained by FOX News.

"If the people aren't getting removed, why the heck are we spending all the money?" asked one former Justice Department official who left with the Bush administration.

Two sources familiar with the memo accompanying the Jan. 16 study said the Justice Department spends at least $20 million each year paying litigators to argue deportation cases in federal appeals courts. But, the former Justice Department official said the total cost to taxpayers is much higher considering the price tag of flying some 300 litigators around the country and putting them up in hotels. That's not to mention the cost for federal and immigration courts to operate so they can hear the cases.

In general, people identified as illegal immigrants first appear before an immigration court, and if they are ordered to leave the country they can appeal that order to the Justice Department's Board of Immigration Appeals and then the U.S. Circuit Court of Appeals. 

About 8,000 cases made it to the U.S. Court of Appeals last year and the study tracked the 7,200 cases in which the Justice Department prevailed. The study found that despite winning those cases, only 1,375 illegal immigrants -- 19 percent -- had been removed as of last month.

"If no one's even doing anything after we win, then what's the point?" the former Justice Department official asked. "We're just spinning our wheels."

The study was initiated by Thomas Dupree, then a top-ranking official in the Bush Justice Department's Office of Immigration Litigation, and conducted with research provided by ICE officials. Dupree authored the memo and distributed it four days before President Obama's inauguration.

ICE spokeswoman Kelly Nantel wouldn't address whether taxpayer money is being put to good use, but she did insist that the situation is more complex than a single Justice Department memo can reflect.

"It wouldn't be accurate to say that we have not followed up on [these cases]," she said. "The entire process is established with the understanding that these individuals have demonstrated their good faith to show up for hearings. They don't represent a threat to the community or a flight risk." She said that anyone in this country who poses a national security threat or a public safety threat is detained.

The Justice Department study and the subsequent memo address only a small piece of a much larger problem that ICE is trying to dent. According to Nantel, 554,000 cases of people inside the United States who aren't complying with an order of removal are currently working their way through the legal system. That's down 12 percent from just a year and a half ago, she said.

However, Nantel acknowledged that among the 7,200 cases studied by the Justice Department, a portion of them could have involved illegal immigrants who ultimately failed to show up as promised. And she noted that when illegal immigrants reach the end of their appeals and are still ordered removed, there is "a very high percentage who fail to show up."

"Now the challenge is addressing those who --- after having access to all the [legal] processes -- choose to abscond," she said.

As part of the legal process, an illegal immigrant can try to "reopen" a case if new evidence in their favor surfaces. But, according to the memo, judges repeatedly asked Justice Department litigators "why an illegal alien is still in the United States arguing his third and fourth motion to reopen in the circuit courts, years after his removal order was issued and became final."

The memo suggests at least one reason: Some illegal immigrants have no place to go. 

"It is our understanding that ICE often faces diplomatic or other obstacles in returning aliens to certain countries, such as China, so in many cases ICE is simply unable to enforce an order of removal owing to factors beyond its control," the memo reads.

The former Justice Department official offered another reason, saying that ICE could try to track down all of the illegal immigrants who failed to comply with a removal order. "But that ain't cheap either."

The memo does suggest limitations to the study's data. For example, some of the 7,200 illegal immigrants cited may have been deported since the end of the study, slightly increasing the number of those removed. 

"There is simply no way to tell for certain, based on the information [provided by ICE] whether many of these aliens are still in the United States, and so we have only counted as removed those individuals that ICE actually identifies as removed," reads the memo.

The memo concludes that "in light of the massive amount of resources devoted to litigating" immigration cases in the circuit courts, the Justice Department and Homeland Security Department should keep track of how those courts' rulings are enforced.

"Doing so will ensure that the government allocates its limited resources in an efficient fashion and is not devoting taxpayer money to adjudications of little practical consequence," the memo reads.