“Alleged” means “suspected.” If a person is an alleged child molester, it means that one or more people have accused him of molesting children. If something allegedly happened, it means one or more people said it happened.
Journalists use the word “alleged” all the time because it gives them a way to talk about things when they don’t have enough information to say for sure whether a guy is a child molester or whether a thing happened or not. You don’t want to say a guy definitely molested children and then find out he didn’t.
The problem is, if you say a guy allegedly molested some children, nobody is going to remember the “alleged” part later, even if he turns out to be completely innocent. The damage to his reputation is done, “alleged” or not.
The other tricky thing about “alleged” is that you don’t have to say who is doing the alleging. Is it the police? An eyewitness? A conspiracy theorist who was high on crystal meth in a soundproof basement two and a half miles from where he says the incident occurred? It could be anyone. This is yet another reason why it’s important to ask questions.