Breakdown of El detective dijo que había interrogado al sospechoso.
que
that / than
decir
to say, to tell
el sospechoso
suspect
haber
(auxiliary) have
Questions & Answers about El detective dijo que había interrogado al sospechoso.
Why do we use había interrogado (had interrogated) here instead of a simple past tense?
Because this is reported speech with a past-tense reporting verb (dijo). When you report an action that was originally stated in the past (like "I interrogated" or "I have interrogated"), the tense shifts back one step into the past perfect (había interrogado) to show that the interrogation happened before the detective spoke.
What were the detective's exact original words before they were reported?
He probably said "Interrogué al sospechoso" (I interrogated the suspect) or "He interrogado al sospechoso" (I have interrogated the suspect). In reported speech, both the preterite and the present perfect change to the past perfect (había interrogado) when the reporting verb is in the past.
Why is it al sospechoso instead of just el sospechoso?
This is a refresher on the "personal a". In Spanish, when the direct object of an action is a specific person (like the suspect), you must put the preposition a in front of it. Since sospechoso takes the masculine article el, the words a and el combine to form the contraction al.
How do we know who did the interrogating if there is no pronoun before había interrogado?
Context! The conjugation había can mean "I had", "he/she had", or "you (formal) had". Based on the first half of the sentence (El detective dijo), we naturally assume the detective is talking about his own actions. If it were ambiguous, you could add él: ...que él había interrogado al sospechoso.