We had a well-known case over here in the UK that is indicative of the difficulties. A man told the police that he had been to gay orgy parties at which young boys had been used for sex, and a couple, killed. He implicated leading figures, including politicians, an army general etc. The police spent several million pounds investigating this, having said that following their initial investigations, they thought it was a valid claim. The alleged perpetrators were all arrested, under caution, interviewed, etc. There was a lot of publicity, homes searched, etc.
Subsequently the allegations were proved to have been completely fabricated, and the man who made the allegations was eventually prosecuted and sent to prison. The police did not seem to realise that the man, Carl Beech, was himself a paedophile.