José María Galante was a leftist college student when he was handcuffed to the ceiling of a basement torture chamber, his body dangling in the air. A police inspector laughed and taunted him, striking martial arts poses before repeatedly kicking and beating his face and chest.

The man who Mr. Galante says tortured him was an infamous enforcer of the Franco dictatorship in the 1970s, widely known as Billy the Kid for his habit of spinning his pistol on his finger. So Mr. Galante was startled last year when he located the man — living in a spacious apartment less than a mile from his own neighborhood in central Madrid.

“How did I feel when I saw him for the first time? We got you now, you bastard,” Mr. Galante said, adding: “I agree with the idea of reconciliation. But you just can’t turn the page. You have to read that page before you turn it.”

This week, Mr. Galante is again planning to see Billy the Kid, whose real name is Antonio González Pacheco. This time, it will be at a hearing at Spain’s National Court, where Mr. Galante and other victims are, for the first time, seeking to prosecute Mr. Pacheco in a case that is reopening the country’s painful Francoist past and threatening the political pact that helped Spain transition from dictatorship to democracy.