I know our immigration system is cracked/broken but

I am really trying to get my head around how this kind of situation happens. It seems to me that there would be a couple of databases that could be checked quickly to avoid citizens being locked in with immigrants. My second question from this article is why are the immigration holds being put in with the main stream prison population?

The cases of two Bay Area men illustrate two of the problems highlighted by the Amnesty report: Detainees often are denied due process, and the burden is on the detainees to prove they don't belong in custody.

Afghanistan-born Lemar Nasir of Fremont and Thailand-born Yuttasak Simma of San Francisco were taken into ICE custody in 2007, though both are naturalized U.S. citizens.

Though the men told immigration officials of their citizenship, neither had papers to prove it, and both languished in immigration custody in Santa Clara County jail - Nasir for 11 months, Simma for seven - before a lawyer finally secured their release.

Sin Yen Ling, an attorney with San Francisco's Asian Law Caucus who represented the men, called the cases a violation of the men's constitutional right to due process.

"Absent congressional authorization, you cannot use immigration laws to lock up a citizen," she said. "And this is not unusual: I have on my docket right now five to seven of these cases. People have legitimate claims to citizenship, and they inform ICE, yet there's no formal procedure to figure out what to do with these folks."