Everyone knows that our immigration system is broken. But one of its worst features remains shrouded in secrecy: Our massive immigration lock-up system.

On any given day, Immigration and Customs Enforcement (ICE) cages approximately 34,000 men, women, and children in jails across the country as it pursues their deportation, at a cost to taxpayers of two billion dollars a year. Scandalously, ICE often has no good reason to incarcerate these people at all. In far too many cases, immigrants are incarcerated even though they pose no danger to anyone, and don't need to be detained to make sure they show up for court. And many of these immigrants—thousands of whom are long-term green card holders—are not actually deportable, as the government claims, but will ultimately win the right to stay in the country.

Perversely, recent data shows that immigrants who go on to win their cases and earn the right to stay here under our laws are especially vulnerable to languishing for months or even years in immigration jail. The Transactional Records Clearinghouse (TRAC), a nonpartisan research center at Syracuse University, analyzed data on immigrants who were released from ICE custody or deported during the last two months of 2012. TRAC found that people released because ICE or an immigration judge eventually found that they were legally entitled to stay in the country had the longest average detention time: 131 days. Moreover, of those who won their cases, 20 percent were detained for six months or more, and the average detention stay for this group was 334 days. In contrast, individuals who were deported spent an average of 27 days in detention.

These nationwide findings are consistent with an expert report prepared by TRAC's co-director, Dr. Susan Long, in Rodriguez v. Robbins , the ACLU's class action lawsuit challenging the long-term detention of immigrants in the Los Angeles area without meaningful bond hearings. Dr. Long's study found that the average length of detention for individuals held six months or longer and who applied for relief from deportation was 421 days.

The data shows just how badly our immigration jails need reform. We should not be wasting taxpayer dollars on incarcerating people for months or years when they pose no threat to anyone and ultimately will be found to have a right to stay in our country. Just like in the criminal justice system, these individuals and countless others can be safely released on bond and conditions of supervision, without the massive costs to taxpayers and devastating harm to families and communities that are the hallmarks of our immigration prison system.