Shouldn't it be por que?
Both work, but preferable "por que"
How to differentiate 'why' vs 'because' in a sentence like this then? just context?
"why" in this case would be "por que".
Isn't "tinham usado" past perfect? I thought this meant "The agents didn't know why they had been using it"
Many times in English we don't distinguish between simple past and past continuous when it involves translating from the portuguese imperfect tense.
I think its pretty confusing that it says "porque" instead of "por que".
could it also be "why they had worn that" ?