In my background, writing police reports, where the suspect was not known. My sentences were often written in pasive voice (at the time I didn't know that was what I was doing). I would write "$1,000 was taken from the cash register."
This is a good point, and another one I was thinking about this morning. You'll often hear passive voice on the news, when the reporters don't have all the information. ("Overnight, the shelter was broken into.") It's very similar to crime and police writing. But like RJK says, there are opportunities to turn it into active voice ("overnight, someone broke into the shelter") but that suggests "blame" again. Oftentimes, passive voice crops up in these situations without the writer even thinking about it.
When it comes to passive voice and fiction writing, it's usually best to be writing in active voice unless you have a good reason to use passive. To build suspense, for example, or when your characters don't have all the information.
"She was murdered," is a passive construction, but if you don't know who or what murdered her, there's not much you can do to make it active. Or maybe you DO know what murdered her, but for suspense's sake you keep it unknown.
Other instances in fiction where I've seen passive voice used are again, during times when the character doesn't know what's happening.
"Jane was peering over the edge when suddenly she was pushed off the cliff." The first "was" in that sentence is not passive. And it's probably okay for the second half of the sentence to remain in passive voice since she doesn't know who pushed her, but there are ways to rewrite it. It all comes down to which version sounds better.
"Jane was peering [or peered] over the edge when suddenly, a pair of strong hands grabbed her by the shoulders and then shoved her off the cliff." Ignoring my poor example, that's one way you could rewrite. Or you can use the stand-by "someone" pushed her over. Or another million rewrites.
In the end, unless you're in business, scientific or police writing, active voice is often the way to go. But passive voice has it's place, too. It's just not as common.