What if the publisher just reporting what someone else said?
The rule is: whoever reports it is liable for it. Even if it’s from an apparently reputable and knowledgeable source, such as the police. The publisher has to prove the truth of the sting of the article, remember. That’s what the readers or viewers will take it to mean. It’s not enough for the publisher to prove that it has reported the accusation accurately. It must be able to prove that the accusation itself is true.
What if the publisher writes “alleged”?
This is just a fancy way of saying “I’m reporting what someone else has said” – so the same answer applies. Sprinkling a story with the word “alleged” or “rumoured” doesn’t insulate the publisher from a defamation lawsuit. The publisher is still passing on someone else’s allegation or gossip.