This just sounds like an overconfident naive man who got duped into being used by a murderer. He thought he was qualified to take this on because he watched Sherlock Holmes and Miss Maples, and he was growing bored of the book he was writing (which he ended up abandoning entirely).

There's just so many gaps in the narrative and jumping to conclusions on circumstancial evidence at best. I'll admit the investigation was not handled properly, but that is surprisingly extremely common. They never said what was wrong with the pathology evidence to dismiss it entirely when the body was already in rigor mortis when found making Robin's timeline extremely unlikely. The only counter evidence provided was his long time friend claiming he heard a female voice call out Robin at a later time, and an anonymous tip claiming a boastful perpetrator that could not be followed up on, oh and a pedophile step father that's long dead. He mentioned Diana wanting to go to the police shortly before the murder but left out explicit mention that there was any evidence it was about the CSA and not something else. The Horizon computer system scandal doesn't fully exonerate him either; at most it highlights that the motive may not have been unconvering fraud/embezzlement. Why did the author not pre-emptively shut down speculation of domestic abuse as is the most likely explanation for this kind of murder? He seems to completely ignore the possibility.

This reads to me like the dumber version of You Can See Everything rather than true investigative reporting. This author is, maybe unintentionally, presenting the most charitable version of events for Robin because he's worried about upsetting or challenging his friend too much. Where's the Amanda Seyfried character to push back here?