Translation:Did he tell the police that he was guilty?
Because the Esperanto sequence of tenses is different from that in English.
In English indirect speech in the past, we move the tense of a verb in the speech backwards in time. In Esperanto, on the other hand, the verb keeps its tense.
What he said was: "I am guilty." or "Mi estas kulpa."
So Esperanto says: Li diris ke li estas kulpa. Note that "estas" did not change the tense -- he said it in the present tense and so when you report it you keep the present tense since you are quoting him.
It's the English that has to be explained :)
Thank you for this explanation but I am still a bit confused. Suppose John tells me that Peter has been arrested and that John knows that Peter is guilty. So, I would then be inclined to say to John: "Did you tell the police that Peter is guilty". I would not say "was" in this instance. How would you translate that into Esperanto? In addition, the Duo sentence is set off in quotation marks and hence should it then not be translated as spoken?
No, it isn't.
si refers to the subject of its verb, so si can never be the subject (or part of the subject*) -- si estas is not possible.
The sentence is ambiguous as to whether e.g. Paul said that Paul was guilty, or whether Paul said that Tim was guilty.
* "part of the subject": this also means that e.g. "Ludoviko kaj sia frato manĝas viandon" is not possible. The subject of "manĝas" is "Ludoviko kaj sia frato", and so if "sia" refers to the subject, it would mean that "sia frato" means the brother of "Ludoviko kaj sia frato"! So, "Ludovico and the brother of "Ludovico and the brother of 'Ludovico and the brother of "Ludovico and the brother of ....." :)
Dear Tmccravy, you ask: "- Did he turn in someone else?" Good question! And the answer could be "yes" (because that would be the normal way to say that)!. Now, if this poor guy wanted to admit that he was himself guilty, the most usual way to say that in Esperanto would be: "Li diris al la polico ke li mem estis kulpa". MEM is the most convenient way to refer to oneself. Now, concerning your idea to use "SI" as a pronoun (and subject of the verb), well, no, as Mizinamo explained it to you!