Miami (CNN) -- It sounded like a good deal: Get a Cuban birth certificate and stay in the United States, worry-free.
But federal authorities say the birth certificates weren't legitimate, and the undocumented immigrants trying to get them weren't Cuban.
Now a federal judge in Florida has sentenced several people for conspiring to commit immigration fraud.
The defendants, authorities say, made more than half a million dollars selling forged Cuban birth certificates to undocumented immigrants and helping them fill out fraudulent U.S. immigration forms.
Their aim, investigators said, was to exploit a U.S. law that allows Cuban immigrants to apply for permanent residence if they've been in the United States for more than a year.
Authorities arrested Nelson Daniel Silvestri Soutto, Laura Maria Ponce Santos, Amelia Osorio and Fidel Morejon Vega last year. Court documents show that all four have pleaded guilty to conspiracy to commit immigration fraud.
Court documents provide details about a type of scam that's becoming increasingly common, immigration lawyers say.
In one conversation with a confidential informant recorded by investigators, Morejon demanded thousands of dollars in payment for Cuban birth certificates and provided advice about how to answer questions from immigration authorities who might ask why he has a Mexican accent.
"'Uh, because I work with a lot of Mexicans and I caught it (the accent) ...'" period," Morejon said, according to a transcript of the conversation filed in federal court. "You are Cuban ... from today on ... 3:25 in the afternoon you are entering the United States and you are Cuban."
Morejon advised the informant and an undercover officer not to make conversation with officials, and to tell them they arrived "in a raft," according to the transcript.
Investigators describe Morejon as the scheme's ringleader, accusing him of recruiting the others and paying them referral fees for each undocumented immigrant who purchased his services.
He "met with numerous illegal aliens and told them that he could assist them in obtaining their residency in the United States by pretending to be Cuban," according to a court document filed along with Morejon's guilty plea agreement last year.
"To effectuate the fraud, Morejon posed as an immigration officer to impress the illegal aliens (and) also threatened some of the illegal aliens with deportation," the document said.
The day authorities arrested him, they found blank Cuban birth certificates and altered naturalization certificates in his Florida home, federal prosecutors said in a memo filed this month. In addition to selling fake Cuban birth certificates, Morejon also sold fraudulent presidential pardons, prosecutors said.
Morejon, of Kissimmee, Florida, is scheduled to be sentenced later this month. Prosecutors have asked the judge to sentence him to more than three years in prison.
"The full extent of Morejon's fraud remains unknown as his former customers continue to be identified by the government," prosecutors said. "The one conclusion that must be drawn from all the facts is that Morejon devoted his life, over a period of more than three and a half years, to extracting as much money as possible from his customers and obtaining that money by whatever means necessary."
U.S. District Judge Cecilia M. Altonaga sentenced Ponce earlier this month to six months in prison, two years on parole and nine months under house arrest. Osorio was sentenced Thursday to four months in prison, two years of parole and 11 months under house arrest. And Silvestri was sentenced to a year in prison, three years on parole and nine months under house arrest.
Morejon pleaded guilty "and acknowledged he was the organizer," said Hugo Rodriguez, an attorney representing Morejon. That means he'll likely receive a higher sentence, Rodriguez said.
Attorney Richard Serafini, who represents Osorio, declined to comment but referred to a memo he filed in court earlier this month, arguing for a lower sentence. The memo argues that Osorio, 61, paid Morejon thousands of dollars for a fraudulent presidential pardon for her son, who had been convicted of a federal drug offense.
She became involved in the conspiracy "through her efforts to help her son" and her criminal conduct was an "extreme aberration," Serafini wrote. "Her background is one of hard work, dedication to her family and, until this episode, law-abiding," the memo said.
Attorneys for Ponce and Silvestri did not respond to requests for comment.
This type of scam has been happening in Florida for years but appears to be on the rise, immigration attorney Wilfredo Allen said.
There are consequences beyond this particular case, according to Maite Hoyos, an immigration attorney in Miami.
More and more, she said, authorities are asking her Cuban clients to prove the validity of their birth certificates -- something, she says, that suggests that this type of fraud is on investigators' radar.
Adriana Hauser reported from Miami. Catherine E. Shoichet wrote the story in Atlanta.