Some claim that sometimes people who are US citizens are also held there.

“My name is Alla Suvorova. I am 25 years of age… From around December 23, 2008, until around January 6, 2009, ICE detained me at B-18… ICE never provided me with any change of clothing… During the entire time that I was in B-18 and in the jails, I was never allowed to go outside.” – such is the personal account of someone who says she was held in “B-18”, an alleged subfield office, tucked in the bowels of a downtown Los Angeles Federal building.

The account claims less-than-humane conditions of detention.

"One of the toilets was stopped up the whole time that ICE held me at B18…The detainees could see me when I was going to the bathroom…I think I slept between 2 to 4 hours each night," Alla says.

Ahilan Arulanantham of the American Civil Liberties Union says they filed a lawsuit against “B-18". Five months later, ICE settled with ACLU to change the conditions.

RT’s crew decided to pay a surprise visit to the famed facility. The center employees let the crew in, but were told that, for reporting on the changes, the head of the media service should be contacted.

"It always acts in a culture of secrecy. It's always a fight to get information,” says Ahilan Arulanantham, “And the detention system is never as transparent as it should be."

But the Otay detention facility was somewhat opened to the filming crew. They gave the journalists a small excursion inside, showing a strictly up-to-code and well self-covered detention center.

"A lot of people don't agree with what we do, but it's a necessary party of the process of enforcing our nation's immigration laws,” says Robin Baker, field office director.

However, the question about the other facilities, the subfield offices and the people who continue to disappear is still to be answered.

"On any given night there will be 40,000 people who will sleep at an immigration detention center somewhere in the country," says Ahilan Arulanantham from American Civil Liberties Union

RT’s American team is preparing a longer, more in-depth report on the allegations.

You can write to feedback@rttvamerica.com to send your suggestions and express your opinions.

Here are the couple of emails on the issue RT has received so far:

David – “I am interested in ICE subfield detention secret offices and would like you to interview to learn more”

Louis – “I want ICE to answer all RT’s questions. This secrecy is a great injustice to the American people”

Michael – “I would appreciate more information with regards to ICE secret prisons in America. Thank you for all you do”

RT is waiting for more emails regarding ICE in order to demand an on-camera sit-down interview with them, in which hopefully they will answer some of these questions.