(CNN) -- Dzhorkhar Tsarnaev, 19, the Boston Marathon attack suspect now at large, came to the United States on July 1, 2002 at age 8 on a tourist visa, a federal source said. While here, he sought asylum and became a citizen on September 11, 2012. His older brother Tamerlan Tsarnaev, another suspect, was killed in a shootout with police. He came to the United States four years later, on Sept. 6, 2006, at the age of 20, the source said. He came legally but was not naturalized. He was a green card holder and in the country lawfully.