I get that they say "a female" because that's how they "identify" people via police reports and such. But I still cringe so bad when I hear someone say "a female".
That's part of it, but police jargon is meant to dehumanize suspects. They could just as easily say man or woman but those words imply person-hood. While animals can be male or female they can't be a man or woman. Male-Black-46 works just as well to describe an animal in a study as a human on the street.