Pedro Guzman has been an American citizen all his life. Yet in 2007, the 31-year-old Los Angeles native — in jail for a misdemeanor, mentally ill and never able to read or write — signed a waiver agreeing to leave the country without a hearing and was deported to Mexico as an illegal immigrant.

“The more the system becomes confused, the more U.S. citizens will be wrongfully detained and wrongfully removed,” said Bruce Einhorn, a retired immigration judge who now teaches at Pepperdine Law School. “They are the symptom of a larger problem in the detention system. … Nothing could be more regrettable than the removal of our fellow citizens.”

It’s impossible to know exactly how many citizens have been detained or deported because nobody keeps track. Kara Hartzler, an attorney at the Florence Immigrant and Refugee Rights Project in Arizona, testified at a U.S. House hearing last year that her group alone sees 40 to 50 jailings a month of people with potentially valid claims to citizenship. “These cases are surprisingly, painfully common,” she said.