Many people who discuss this case may be helping to propagate a classic double-error. I have no idea if Stone did this, but let's just assume he didn't and he's innocent. It does not follow that Bellfield is guilty. By assuming this by default, even on a speculative basis, you may be falling into the same terrible trap as the police. It's a bugbear for me whenever I am among true crime aficionados and miscarriage of justice campaigners who want to adopt this cut-throat approach. Clearly Bellfield is not a nice man, but he may be entirely innocent of this terrible crime, and if Stone is also innocent, it could be that the real killer has never been caught - and may never be caught.
It's said that Bellfield admits he was in the area, but that does not make him guilty. For one thing, why would he be so honest if he were guilty? It may also be that he wasn't in the area at all and he is just attention-seeking.
When I first heard about this case years ago, I immediately wondered why the father was not a suspect. The explanation for this seems to be that Josie Russell got a good look at the attacker and gave a description that is assumed to be a third party, thus the father is exculpated. I recall reading somewhere (unfortunately, I can't now recall the source) that Josie or someone else remarked that the attacker resembled her father, but just to add important context: that wasn't said to cast any suspicion on the father, rather it was to aid the physical description by way of a comparison with somebody she knew. Her description does sound like Bellfield in the sense of 'chubby face' and 'spiky hair', and that does not sound like Stone.
Interestingly, Josie said that the attacker wasn't masked, yet he did not initially intend to kill them, which suggests he didn't plan it. So what was he doing? Robbing them perhaps? But do illicit drug-takers and other wrong-doers generally seek to rob middle-aged women with young children in the middle of nowhere, or anywhere?
Josie was 9 years old at the time, and had suffered brain injury, yet at some point on her road to recovery she attended (by video link) an identification parade at which she failed to identify Michael Stone.
The e-fit of the killer is not from Josie, but from another witness who saw some random person driving away from the same location. That witness, too, failed to identify Michael Stone at a police-arranged identification parade. Thus, the e-fit identification is not reliable at all. It is based on putting 2 and 2 together by a woman who could not identify Stone when face-to-face with him (albeit she claimed he looked familiar). This suggests to me that Josie's description is the one to be relied on - allowing for the inevitable imperfections.
Another thing about the e-fit is that everybody lazily says that it doesn't look like Stone but does look like Bellfield. I disagree. It does look like Bellfield, but it also resembles Stone - if you look closely at it and take the mental blinkers off. Now consider the fact that Stone and Bellfield are entirely dissimilar in physical appearance, both then and now. This only reinforces the unreliability of the e-fit - but, perhaps, only viz. Stone and Bellfield. Perhaps, going against what I say above, the e-fit is true and the conviction and suspicion are wrong?