By JAMES C. McKINLEY Jr.
 
MEXICO CITY, Jan. 4 - Aleida Gallangos was 2 years old when the police arrested her parents after a gunfight and then spirited away her brother, who had been shot in the leg. Her mother and father disappeared into jail and never came out, like hundreds of other leftists erased from history during the ugly underground war here in the 1970's. She was adopted by another family.

What happened to her brother, who was 3 when he disappeared, remained a mystery until last week, when Miss Gallangos, after a three-year search, found him living in Washington, D.C., working in construction under a different name.

It took Miss Gallangos, who is 31, several days of talking to her brother on the telephone to convince him of his identity. Finally, the 33-year-old man born Lucio Antonio Gallangos walked into an apartment where she was staying, embraced her and accepted his own past.

The reunion of the brother and sister who lost each other in a gunbattle three decades ago is a bright footnote in the dismal history of Mexico's clandestine war against leftists. Miss Gallangos's brother, who goes by Juan Carlos Hernández, is the first of more than 500 people known to have disappeared in Mexico's "dirty war" to be found alive, largely because of her efforts to trace him.

"I did it simply because he is my brother, because I wanted to see him, to know how he was," Miss Gallangos said. "I wanted to know if he was alive, if at any time he had suffered torture. I didn't even know if he was alive or dead."

Miss Gallangos, a midlevel manager at a factory in Ciudad Juárez, is one of hundreds of people in Mexico trying to piece together family histories torn to shreds by the disappearances. She tracked down her brother using baby pictures, orphanage photos, adoption records, telephone books and a captured number on her caller ID, which led her to the Washington area. The biggest obstacle was the reluctance of his adoptive parents to disclose where he lived, she said.

Along the way she got help from Mexican prosecutors investigating the disappearances, television reporters from Univision, and the editors of the newspaper The Washington Hispanic, who published several articles appealing for help and paid for a private investigator. Finally, on Dec. 23, Univision broadcast an item about her search. The next day, Christmas Eve, her long-lost brother called her.

"Who are you looking for?" he asked. And she told him his own story.

It was a story she herself had learned only a few years ago, after President Vicente Fox took office in 2000, opening to the public classified documents about the purges of leftists.

Miss Gallangos, who grew up with the adopted name Luz Elba Gorostiola, discovered her paternal grandmother, Quiriña Cruz, through a magazine article about people who had disappeared at the hands of the state police. Her grandmother had been fighting for years to find out what had happened to her sons, Roberto and Avelino Gallangos; her daughter-in-law, Carmen Vargas; and two grandchildren.

In June 1975, the police raided a house where the Gallangos brothers and Carmen Vargas were staying with the children. A gunfight broke out. The Mexican authorities suspected that the brothers were members of a communist terrorist group, the Red Brigade of the Sept. 23 Communist League. The police believed they had been involved in bank robberies to finance terrorist activities, according to a report by the National Commission on Human Rights.

The three adults were taken into custody after the gunfight. The police took the boy, Lucio Antonio, to a local hospital to be treated for a leg wound, then transferred him to an orphanage, La Casa Cuna de Tlalpan, under the name "Antonio N." He was adopted a month later by Rosendo Hernández López.

As Roberto Gallangos and his wife were being carted off to jail, they gave their 2-year-old girl to a friend of the Gorostiola family, which later adopted her. She was not told of her origins until she was 16 years old.

Juan Carlos Sánchez Pontón, a deputy special prosecutor investigating the disappearances, said that what happened to Mr. Gallangos and his wife was still unknown. They were last seen alive in a Mexico City jail in 1975. He said his office had identified at least four former officials who participated in detaining them and placing their son in an orphanage, but no one has yet been charged with a crime.

Miss Gallangos said she did most of the detective work to find her brother. A lucky break came in February, when a file photo was discovered of a boy admitted to La Casa Cuna orphanage in June 1975 who looked remarkably like her father.

Mr. Hernández, a construction worker, said he was stunned by the revelation that the people who had raised him as their son were not his parents. His adoptive father and mother never told him he was an orphan and tried to protect him from Miss Gallangos's inquiries. He said that the news had been hard on his family and that he was struggling to come to terms with it himself.

"Despite the fact that I come from the Gallangos, I have a complete life with another family; for me no other family exists apart from them," he said in a telephone interview.

As for their parents, Miss Gallangos harbors no hope that they are alive, or even that their bodies might be found. Since President Fox appointed a special prosecutor in January 2002 to investigate the disappearances, the government has had little success in obtaining indictments against past government officials or even locating the missing.

"I think we have a right to know the truth," Miss Gallangos said.