I thought of that as I read.

But I couldn't come up with any way for the writer to prove that they were a cop, without exposing themselves and their family to retaliation.

Things are going to get worse before they get better. If I were the writer, I too would jealously guard my anonymity. I would agree that the anonymity damages the value of the article; but I would place my family's safety far above that.

(But have a couple of claps anyway.)