You're a Hogwarts student, you don't have hindsight and access to the same level of information than the reader about the ministry cover up. You do know Harry is kindhearted and doesn't chase attention. However you also witnessed him fainting in divination class and screaming about his scar hurting and having visions.

Harry returns from the labyrinth with Cedric dead. He screams Voldemort is back and that Cedric, as a corpse, asked him to return his body to Hogwarts. Which in itself seems incoherent if you're not told about priori incantatem.

Dumbledore reveals the true story but the ministry said Harry is unstable and subject to visions. Cedric death was an unfortunate accident and Harry instability made he think it was a conspiracy by a Dark Lord who killed his parents 14 years ago. That Dark Lord had vanished since.

So who do you believe?

Personally, knowing Harry I wouldn't believe reports he's lying for attention. However I would wonder if his scar crisis/visions, and ultimately PTSD, may have clouded his version of a traumatic event.

Ultimately, given Harry good reputation I would give him the benefit of the doubt and side with him.