The indictment of Manuel Rocha, the former U.S. ambassador accused of working for Cuba’s spy service for decades, has left longtime colleagues struggling to make sense of what was real and what was deception in a life that straddled poverty and privilege.

The journey that led Mr. Rocha, 73, to the top echelons of the State Department began in Harlem in the 1960s after he and his mother, a widow who worked in a sweatshop and relied on food stamps and welfare, emigrated from Colombia, according to an account he provided years later.

A life-changing break came in 1965, when Mr. Rocha won a scholarship to attend the Taft School, an elite boarding academy in Connecticut that unlocked a string of academic and career opportunities, including an Ivy League education and influential government jobs overseas.

The transition at times made him feel like an outsider. For instance, according to his account to the school’s alumni magazine, Mr. Rocha’s best friend refused to become his roommate because of his ethnicity.

“I was devastated and considered suicide,” Mr. Rocha told the magazine in 2004, shortly after he had retired from the State Department.

Since his arrest a week ago, friends and former colleagues have expressed shock as they absorbed the allegations in a federal indictment that Attorney General Merrick Garland said details one of the “highest-reaching and longest-lasting” national security breaches in generations.