Ninety-eight percent of those arrested between Oct. 1, 2000, and Sept. 30, 2005, were never prosecuted for illegally entering the country, according to an Associated Press analysis of federal data. Nearly 5.3 million immigrants were simply escorted back across the Rio Grande and turned loose. Many presumably tried to slip into the U.S. again.
The number of immigrants prosecuted annually tripled during that five-year period, to 30,848 in fiscal year 2005, the most recent figures available. But that still represented less than 3 percent of the 1.17 million arrests made that year. The prosecution rate was just under 1 percent in 2001.
The likelihood of an illegal immigrant being prosecuted is "to me, practically zero," said Kathleen Walker, president-elect of the American Immigration Lawyers Association.
Federal prosecutors along the nation's southern border have come under pressure from politicians and from top officials in the Justice Department to pursue more cases against illegal immigrants.
But few politicians are seriously suggesting the government prosecute everyone caught slipping across the border. With about 1 million arrests made each year, that would overwhelm the nation's prisons, break the Justice Department's budget and paralyze the courts, immigration experts say.
The Justice Department itself says it has higher priorities and too few resources to go after every ordinary illegal immigrant. Instead, the department says it pursues more selective strategies, such as going after immigrant smugglers and immigrants with criminal records.
T.J. Bonner, the union chief for Border Patrol agents, said the most effective solution would be to dry up job opportunities in the U.S. by cracking down on employers who hire illegal immigrants.
"The employers are the ones breaking the law," he said, suggesting the creation of an "idiot-proof" system to check the immigration status of workers and the prosecution of any employers who knowingly hire those in this country illegally.
"It's much like our tax laws: People don't pay their taxes out of an overriding sense of citizenship; it's a healthy dose of fear," Bonner said.
Under federal law, illegally entering the country is a misdemeanor punishable by a fine and up to six months in prison for a first time. A second offense carries up to two years. If an immigrant has been prosecuted and deported and then sneaks back into the country, he can be charged with a felony punishable by up to two years behind bars. Those with criminal records can get 10 to 20 years.
The federal figures on arrests and prosecutions were collected and provided to the AP by the Transactional Records Access Clearinghouse at Syracuse University in New York.
Justice Department spokesman Dean Boyd said in a statement that 30 federal prosecutors have been added to the Southwestern border to handle the rising number of immigration and border drug cases and noted that securing more prosecutions would require hiring more judges and public defenders and building more courtrooms and jails.
Authorities also note that illegal immigrants who make it past the border are not necessarily home free. In the past year, immigration officials have conducted numerous raids on workplaces.
Boyd noted that the Border Patrol can charge illegal immigrants with civil violations punishable by fines of $50 to $250. But Border Patrol officials said most Mexican immigrants are not sent before a judge to be fined.
"The majority are offered and granted ... voluntary removal back to Mexico," said Xavier Rios, an assistant chief Border Patrol agent in Washington. "We don't seek to prosecute everyone."
Boyd said the Justice Department pursues charges if a case involves human smugglers, if an immigrant has a felony record in the U.S., or if he has been deported before.
"When you consider the other high-priority laws that the department is charged with enforcing, such as drug trafficking, firearms offenses, violent crime, national security, child pornography, and corporate fraud, the department is achieving a balance of immigration enforcement with other important areas," Boyd said.
Last month an undated internal Justice Department memo released as part of the congressional investigation of the firings of eight U.S. attorneys revealed that in Texas, most illegal crossers have to be caught at least six times before their case will be forwarded to prosecutors.
Still, some border regions have decided to crack down.
Along the Border Patrol's 210-mile Del Rio sector in West Texas, any illegal immigrant arrested since 2006 is jailed and prosecuted, under a federal project called Operation Streamline. It was briefly repeated along a narrow stretch of border in New Mexico. And Maricopa County, Ariz., officials are using a state anti-smuggling law to prosecute both suspected smugglers and the immigrants who pay them.
Rep. Ted Poe, R-Texas, a former state judge, said that the prosecution rates amount to "dereliction of duty" and that the government should spend whatever it takes to lock up and deport every illegal immigrant.
"Prosecutors should not have the discretion to prosecute some people for violations of the law and not others, that's discriminatory," he said.
But Iliana Holguin, executive director of the El Paso Catholic Church's Diocesan Migrant and Refugee Services, said that would mean the government would have to "massively increase the size of the court system, or it is going to collapse on itself under its own weight."
Holguin suggested changing the immigration laws instead to make it easier for workers to enter the United States legally.
"It's not a light decision to come to the U.S. illegally," she said. "If there was a legal way to fill these labor shortages or reunite families, they would do it."