The U.S. government has quietly created a second-class federal prison system specifically for immigrants. For years the Department of Homeland Security has been known as the agency that houses immigrants awaiting deportation. However, tens of thousands of additional immigrants, most serving sentences for immigration crimes, are held by the Bureau of Prisons each night before being sent back.

And it’s all part of a lucrative business model which has funneled billions of taxpayer dollars into the private prison industry.

A Fusion investigation found that without a single vote in Congress, officials across three administrations: created a new classification of federal prisons only for immigrants; decided that private companies would run the facilities; and filled them by changing immigration enforcement practices.

"You build a prison, and then you've got to find someone to put in them,” said Texas state Sen. John Whitmire, who has seen five of the 13 Criminal Alien Requirement (CAR) prisons built in his state. “So they widen the net and find additional undocumented folks to fill them up"

Most of the roughly 23,000 immigrants held each night in CAR prisons have committed immigration infractions -- crimes that a decade ago would have resulted in little more than a bus trip back home. And now, some of the very same officials who oversaw agencies that created and fueled the system have gone on to work for the private prison companies that benefited most.

The low-security facilities are often squalid, rife with abuse, and use solitary confinement excessively, according to advocates.

Built in remote towns across the country, these prisons hold nearly twice the number of inmates in solitary confinement as other federal facilities, an American Civil Liberties Union report found. Inmates are allegedly placed in solitary confinement for complaining about food, medical care or filing grievances.

At one prison in Texas, officials placed a 32-year-old-man with epilepsy in solitary confinement to allegedly provide him with extra medical attention. However, the man died weeks later in solitary without enough medication in his system and without medical supervision, according to the man’s family who later sued the government and the company that ran the prison.

Immigration-related offenses make up the majority of convictions for immigrants in the federal system

Roughly two-thirds of immigrants who serve time in the federal prison system are locked up for “illegal reentry” -- an offense that was once rarely prosecuted. In 2005, that changed. The federal government decided to ramp up prosecutions under an internal program called Operation Streamline and the number of cases has risen over 183 percent since its implementation, with an average sentence of 18 months behind bars.

Prosecutions for "Illegal Reentry" have risen over 183% since 2004

Federal criminal prosecutions for illegal re-entry

The ramp-up in enforcement prompted a spike in immigration beds across three federal agencies. Today, the Bureau of Prisons’ contracts provide more taxpayer dollars to private prison companies than facilities run by Immigration and Customs Enforcement. In the last five years, the two largest prison companies have made nearly $2 billion in revenue from their CAR prison agreements.

In the years leading up to the crackdown, private prison companies spent more money than ever lobbying the federal government. The two largest companies -- Corrections Corporation of America (CCA) and The GEO Group -- have also long supported elected officials whose legislative efforts result in more business for them. Both companies insist their lobbying dollars focus on promoting their services and not shaping laws.

“To be clear, neither CCA nor its federally registered lobbyists have ever lobbied specifically or directly for or against Operation Streamline,” a CCA spokesperson wrote in an email.

Judith Greene, the director of a Brooklyn-based criminal justice think tank Justice Strategies that has tracked the growth of the prisons, disagrees.

“It’s an oversimplification to say private prisons single-handedly created the system we have now,” said Greene. “But they are enablers and more than just that because once they enable they are clearly pushing for more -- despite what they'll tell you."

An analysis of contracts obtained by Fusion found that private prisons charge roughly between $50 and $75 a day for each immigrant they hold. The companies make between 20 percent and 30 percent in profit on each bed, according to market research estimates by CRT Capital Group.

These profits are passed on to company leadership. Executive positions at the prison companies pay much better than those in government. Three out of the last four Bureau of Prisons directors now sit on the boards of the biggest prison companies.

Many other government officials at the Department of Justice and Department of Homeland Security who were in charge when Operation Streamline was implemented and immigrant prisons were built now work in the private prison industry. They joined other former officials who had already made the move.