"Os agentes não sabiam porque tinham usado isso."

Translation: The agents did not know why they had used it.

[DominoD87]

Shouldn't it be por que?

[Paulenrique]

Both work, but preferable "por que"

[Trianaea]

How to differentiate 'why' vs 'because' in a sentence like this then? just context?

[Paulenrique]

"why" in this case would be "por que".

[Jake50389]

I think its pretty confusing that it says "porque" instead of "por que".

[Marie-Anne227031]

could it also be "why they had worn that" ?

[deactivated user]

Yes, as in they wore an odd disguise. I've reported it. Duo should fix it in, oh, six or seven years. :/

[KrisKalis]

Sabiam? That's not what she pronounces at all! I hate this woman so much.

[querofalar12]

Isn't "tinham usado" past perfect? I thought this meant "The agents didn't know why they had been using it"

[deactivated user]

Many times in English we don't distinguish between simple past and past continuous when it involves translating from the portuguese imperfect tense.