It’s a legalism. Until convicted by a court of law, the press has to refer to him as the “alleged” or “suspected” killer. . .
Is this a federal law, state law, administrative rule, or are you just an amateur making stuff up?
It’s common sense in a toxic legal environment. If claimed by the press to be the killer, and if somehow found innocent by a court of law, he can claim and sue for libel.
Remember, you are not PROVEN to be guilty before convicted by a court of law. Even if everyone knows the facts, even if it was on live TV. . .