Prigioniero vs. detenuto
While both prigioniero and detenuto refer to someone deprived of their freedom, they are not interchangeable. The difference lies in the context of the confinement: one is a legal and administrative term, while the other relates to war, captivity, or metaphorical situations.
Prigioniero
B1A prigioniero is a captive, most commonly a prisoner of war (POW). This term is used when someone is captured and held by an enemy force, kidnappers, or in situations outside the formal justice system. It can also be used metaphorically to describe someone who feels trapped.
Il soldato fu catturato e tenuto prigioniero dal nemico.
(The soldier was captured and held prisoner by the enemy.)
Lo scambio di prigionieri avverrà al confine domani mattina.
(The prisoner exchange will take place at the border tomorrow morning.)
I rapitori tenevano l'ostaggio prigioniero in un seminterrato.
(The kidnappers held the hostage prisoner in a basement.)
Dopo il naufragio, rimasero prigionieri sull'isola deserta per mesi.
(After the shipwreck, they remained prisoners on the deserted island for months.)
Si sentiva prigioniero della sua stessa routine quotidiana.
(He felt like a prisoner of his own daily routine.)
Detenuto
B2A detenuto is an inmate or a detainee. This is the official, legal, and administrative term for a person held in a state facility like a prison or jail. Their confinement is the result of a legal process, such as an arrest, a trial, or a conviction.
Il detenuto sta scontando una pena di dieci anni di reclusione.
(The inmate is serving a ten-year prison sentence.)
Ogni detenuto ha diritto a un'ora d'aria al giorno.
(Every inmate is entitled to one hour of yard time per day.)
Un detenuto è evaso dal carcere di massima sicurezza.
(An inmate has escaped from the maximum-security prison.)
L'uomo è attualmente detenuto in attesa del processo.
(The man is currently detained awaiting trial.)
Le condizioni di vita per i detenuti in quella prigione sono molto dure.
(The living conditions for the inmates in that prison are very harsh.)
Summary
In essence, use detenuto for an inmate within the official justice system (prison, jail). Use prigioniero for a captive in a war, a hostage situation, or in a metaphorical sense of being trapped. A detenuto is held by the state following legal procedures, while a prigioniero is held by an opposing force or circumstance.