The answer: There's no way of knowing. And that, in a nutshell, is the potentially insidious nature of what is called the passive voice.
The passive voice allows a writer or speaker to completely sidestep a crucial question like who, exactly, performed a certain act.
The coffee was made. The car was stolen. The employee was fired.
Made by whom? Stolen by whom? Fired by whom? The writer isn't saying. At times that's fine, but other times it can be a serious disservice to the reader.
The passive voice is created with a form of "to be" such as "is," "was" or "were," followed by what's called the passive participle, which is identical to the past participle. So in "the coffee was made," the verb "was" and the passive participle "made" combine to make this passive voice.
A lot of people think that passive voice is a sentence with a lot of "ing" forms — like "Gloria was considering becoming more loving and caring." Others think it's any sentence in which the action is snuffed out: "Joe had become convinced that throwing the ball was the thing to do." But in fact, both these sentences are in the active voice.
Instead, passive voice is something quite specific. Simply put, passive voice occurs when the object of an action is made the grammatical subject of a sentence. (More precisely, you'd say it's when the object of a transitive verb is made the grammatical subject of a sentence, but for anyone who finds that too jargon-y, stick with the former definition.)
Consider the sentence: Barb made coffee. This is a classic example of active voice. The doer of the action, Barb, is the subject of the sentence. The thing being acted upon, the coffee, is the object of the verb "made."
