Learn Italian: L'investigatore ha interrogato il complice. - The investigator interrogated the accomplice.

This lesson is about expressing doubt with che and the subjunctive. How would I rewrite this sentence to mean "Could the investigator have interrogated the accomplice?"

You would use che followed by the past subjunctive, since the original action took place in the past. The sentence becomes: Che l'investigatore abbia interrogato il complice?

Is the verb interrogare used exactly like "interrogate" in English?

It includes criminal interrogations, but it's much more common in everyday Italian life! In schools, interrogare is the standard verb for a teacher calling on a student for an oral exam. A student might say, Oggi il prof mi ha interrogato (Today the teacher tested me).

I noticed complice ends in -e. How do I know its gender?

Complice is a noun whose singular form is the same for both men and women. You look at the article to know the gender: il complice is a male accomplice, and la complice is a female accomplice. The plural forms are i complici (masculine) and le complici (feminine).

How would I rewrite this to say "The investigator interrogated him"?