GR is the only person in the world who has been fully ruled out as a suspect. The police went out of their way to make this clear in a way they hardly ever do.
His alibi was of a kind allowing for multi-point verification and there is no credible way that the police either forgot to verify it or got it wrong. And I don't say that because the police are infallible (they're not), but because they are not completely incompetent.
It has been pretty clear from the start that the perp who was being looked for, who fitted the facts, and who was being hinted at by those best placed to have ideas, was someone very local but not Greg. CJ, PS and VT were more or less credible candidates. MW wasn't because he too had the kind of alibi that can't be faked.
The arrest of VT has several characteristics suggesting the police have much stronger grounds for suspicion than in the case of CJ. They also have the testimony of TM which will no doubt be highly important.
They also have CJ's testimony - assuming he didn't spend 54 hours saying "no comment", which doesn't look like his style. And it may already be that CJ and VT have offered mutually exclusive defences, IYSWIM.