This is part two of a five-part series looking at how illegal immigration affects U.S. border security, the criminal, health care and education systems, as well as the economy. Watch the series this week on FOX News Channel.
Many police officials in states along the U.S.-Mexican border say they are fed up with the number of illegal aliens populating American prisons, many of them incarcerated for violent crimes such as murder, rape and robbery.
Almost one in six inmates in Arizona, for example, is a Mexican citizen.
"It is a phenomenon that law enforcement recognizes as a major problem," said one undercover detective, who specializes in street gangs and goes by the name "Paco."
"We have to put drug users and violators in there, babysit them, and now we have to babysit illegal aliens," said Maricopa County (search), Ariz., Sheriff Joe Arpaio (search), whose jails are 4,500 inmates over capacity.
Most Mexicans cross the border looking for work, but competition is fierce for jobs requiring uneducated, unskilled labor. Many illegal immigrants find themselves far from realizing their dreams.
"We come over here to find a better life," said inmate Tony Perez, a convicted drug dealer. "Not all of us are here to sell drugs or to do bad things, despite a few that do. But then again, doesn't everybody else from every other country?"
Arpaio's Phoenix jails (search) house 1,200 criminal aliens, including Perez, who by law should have been deported. But because of federal bureaucracy and an overburdened system, only the most dangerous felons are actually sent home.
Even when deportation is ordered, about 60 percent of orders are ignored.
Christian Higuera, who is serving time for assault, has fathered an illegitimate child, born in Arizona. He said he hopes he will be allowed to stay with his child, an American citizen, once he gets out of jail.
The borders are so porous that many deported criminals simply come back into the United States, often to commit more crimes.
"If somebody has a proclivity for criminal activity already established, they will continue in that vein," said Paco.
In Los Angeles, 95 percent of all outstanding homicide warrants and 60 percent of outstanding felony warrants are for illegal aliens.
American taxpayers are paying for the crimes of the 8,000 convicted aliens not yet caught and the incarceration costs of those who have been.
That adds up to more than $1 billion a year — in just the states that border Mexico.
The third installment of this series focuses on how Los Angeles' public health care system is overwhelmed by the uninsured and illegal immigrants. Look for it on FOX News and FOX News.com.
Click on the video box above for a complete report by FOX News' William LaJeunesse.