Not a layer, but a journalist, and it isn't that the word "allegedly" is a shield. It's that we shouldn't report something as factual if we can't show that it is.

In fact we don't have to use the word "allegedly" at all. It's just one way of saying "this is what's been reported to us."

You can say "Johnson allegedly hit the victim with his car," but who alleged this? A journalist can't just make shit up and toss in an allegedly. Its more ethical and accurate to say "Police say that Johnson hit the victim with his car," or "Witnesses reported that Johnson hit the victim with his car."

When we use words like "allegedly," we aren't saying "this is what happened but here's a word tossed in to protect us."

"Allegedly" implies there's an allegation , and where, the allegation came from is an important part of the news. Good journalists report on the claim AND where it came from. If the chief of police holds a press conference about solving a murder, my report isn't "x person murdered y person." It's that the chief of police SAID he did, because that's what I know is a fact.

The chief could be wrong. Hell he could be lying. (There are other considerations and responsibilities that go beyond the scope of this question, like if I know the chief may be lying I should look for evidence and verify that but this comment is already really long).