U.S. immigration officials shipped Guzman to Tijuana in May 2007 from the Men's Central Jail in downtown Los Angeles, where he was being held on a misdemeanor trespassing charge. The Los Angeles native, then 29, spent three months rummaging for food in dumps and sleeping in the Mexican borderlands as his desperate mother, a fast-food cook, searched for him in hospitals, shelters, jails and morgues, his family said.

Eventually Guzman, a cement finisher with limited Spanish and a second-grade reading ability, was reunited with his family in the border town of Calexico.

The Guzman case sparked Washington hearings at which immigration authorities were chastised by Congress members and accused of "stunning incompetence." ICE officials called the case an aberration and vowed to review all citizenship claims before anyone was detained or deported.

Out of more than 1 million detentions, ICE officials say, Guzman was the only citizen known to have been shipped out of the country. But others dispute that claim.

Rachel E. Rosenbloom, supervising attorney at Boston College's Post-Deportation Human Rights Project, cited at least eight cases of wrongly deported citizens and said she expected the number was substantially higher.

One such case, detailed in an upcoming report by Rosenbloom's group, is the curious saga of Duarnis Perez. He is a native of the Dominican Republic who became a U.S. citizen at 15 when his mother was naturalized. But he didn't know citizenship had been conferred on him as well. He assumed he was illegal, and so did everyone else.

Perez was deported and subsequently arrested trying to sneak back into the United States from Canada. He spent almost five years in prison for unlawful reentry. It was only upon his release in 2004 that an ICE official reviewed his file and informed Perez that he had been a citizen all along.

In Castillo's case, he was an infant when his mother left Belize and sought work in Los Angeles. She later became a nurse and sent for her son. Castillo attended elementary school in South L.A. and graduated from Thomas Jefferson High School in 1996. He became a naturalized citizen in 1998. He joined the Army and served in Korea, then was posted to Ft. Lewis, Wash. He was honorably discharged in 2003.

After domestic disputes with a girlfriend, he was convicted in 2005 of felony harassment and violating a no-contact order, and was sent to Pierce County Jail in Washington state for eight months. He was in a holding area with inmates about to be released when a corrections officer held him back.

Castillo was handcuffed and whisked off in a van to the Northwest Detention Center in Tacoma. A federal officer said records showed he was an illegal immigrant.

"Your records are wrong," Castillo said he replied. He said he told the officer that he was a citizen but that his naturalization certificate had never arrived. It was sent to the wrong address, he later learned.

Castillo went before an immigration judge, who appeared via video conference, a common procedure in the crowded immigration court system. Again, he claimed citizenship. The judge didn't believe him. He was ordered deported on Jan. 24, 2006.

The nonprofit Northwest Immigrant Rights Project, a legal advocacy center based in Seattle, provided a lawyer to handle Castillo's appeal. The lawyer searched for Castillo's naturalization documents and records of his military service.

The Board of Immigration Appeals blocked Castillo's deportation, noting proof of his military service. A month later, he was released without further explanation. It turned out Castillo was the victim of a paperwork mix-up: His name was spelled wrong in immigration records. And he had been assigned more than one "alien number," causing further confusion.

Castillo, now 31, is still incredulous.

"If it had taken 30 days to figure it out, I wouldn't be upset. But seven months?" he said in an interview.

He, like Guzman and others with similar experiences, has filed suit against the ICE.

"I want them to recognize they made a mistake," Castillo said. "Something needs to change. If it can happen to me, it's going to happen to someone else."

patrick.mcdonnell@ latimes.com

abecker@cironline.org

This story was reported and written in collaboration with the Center for Investigative Reporting in Berkeley, a nonprofit news organization. Andrew Becker is a CIR staff reporter. Patrick J. McDonnell is a Times staff writer.