I agree Floraclara. There is a simple narrative that makes absolute sense.
RG broke in order to burgle the place, he was disturbed by Meredith, he assaulted and killed her, left his DNA everywhere, left bloody hand and footprints, stole her mobile phone and disposed of it in a nearby garden, ran to a friend's house and then a nightclub to create an alibi.
After a couple of days he fled to Germany and was then arrested. Once he realised that the police were interested in RS and AK, he come up with a story that implicated them. He could not dispute the DNA evidence, so he confessed, got a fast track trial and reduced sentence.
RS and AK then found themselves in the weird world of prosecutor Mignini (see the Monster of Florence case for background on him) who dreamt up the sex game scenario with no evidence to support it.