Márcio, I don't recall where I found the book.  Possibly I got it at a very weird bookstore on the Santa Monica Promenade.   The book was written, I believe, by a professor at the University of Oklahoma.  It's very interresting and full of examples. 

At the Santa Monica bookstore I definitely found a giria dictionary.

Most people are satisfied that Cassidy and Sundance were killed in a town called San Vincente in Boliva.  (There are about 5 towns with that name, by the way.)  If so, their remains were not recovered.  As I recall, however, the remains of two other non-Indian, non-Hispanics were found and underwent DNA testing.  Apparerently, American bandits were not uncommon in South America.

I'm inclined to believe that both men returned to the USA.  There was a man in Spokane, Washington, who wrote a movie script about one of Cassidy's train robberies.  He looked very much like the man in Cassidy's photos.  Many people believed that he was Cassidy.  Cassidy's sister says the Spokane man was not her brother.  Cassidy, she said, died of a lung ailment in Oregon.  She would not give the location of his grave.  In view of her own death, it would be pointless to ask her again.  The man from Spokane was cremated and his ashes were scattered over a river, I believe.  Several friends of Cassidy also claim that they talked with her brother about 20 years after his alleged death in Bolivia.  I've heard historians claim that Cassidy's friends had been fooled by an imposter.  That sounds ridiculous to me.  I've come across old friends after years of not seeing them. and I had no trouble recognizing them.  You probably have too.  No, I think he returned.  As for Sundance, people claim to have seen him in the USA long after the Bolivia incident.  Some believe he died about 1930 and lies buried in New Mexico.  His real name, as I recall, was Harry Longbough.  Longbaugh?  He got the nickname Sundance (the Sundance Kid) for having served a term in the Sundance jail.  As I recall, he was not a close friend of Cassidy while in the USA.  No, Cassidy's closest friend in the USA was Harry Logan.  Nothing is known about Etta Place.  She appeared out of nowhere, went with them to South America, returned to the USA, and vanished.  She is truly a woman of mystery.