With respect I just feel this is too much of a conspiracy theory you're hinting at.
No problem i can completely see where you're coming from.
I just don't see how they could so skillfully have set him up if it was actually someone else that did this.
I don't see it as a skillful set up either as, to my mind, there are holes all over the place but it requires a very cynical mind to perceive things that way i agree.
He was crying and threatening to self harm that night
This could be down to teenage angst and is not too uncommon i would say. Also, his friend testified that after a while he had pulled himself together and said he was fine. I'm not sure any of this correlates to what supposedly happened later.
then he's seen going out of his house 3 times with different clothing on etc and with a torch.
He does explain this but, i agree, going in and out of the house at such a time may cause suspicion. He doesn't look like he had just committed an horrific crime though. If he wasn't going out to dispose of evidence, hide the body or retrieve the knife then i don't know exactly what he was meant to be doing.
Also, it doesn't rule out the fact that he was going out to, for example, help somebody else involved with the murder if one wants to go down that road.
His DNA all over the body,
It's easy to say this but exactly what DNA? Was his sperm all over her body or his hair or his saliva? This has not been made clear but it seems from best guess that they are hinting at his sperm is all over her. How did this come to pass? If the dna on her neck and face was sperm then that is, imo, more likely to come from someone using, say, a condom full of sperm and smearing it around and inside the privates. The residue from such an act would remain on the perps hands and be transferred to the rest of the body during the remainder of the crime.
AM's DNA was not over any of AC's clothes or in his bathroom where he went immediately after the crime. There was none of the usual tell tale signs like AC's skin under AM's finger nails either, for example.
CCTV of someone carrying a person down by the shore.
Nobody has ever confirmed that the image showed anyone carrying a child, just that they were carrying something.
Nobody has ever confirmed that the CCTV is of AC.
Nobody has ever confirmed whether it was a man or a woman on the CCTV.
On the one hand AC is so cunning and clever that he chooses his routes carefully to avoid CCTV and other people. On the other hand, he walks right past the CCTV of members of his victim's family. While on the beach he leaves a knife there right opposite his victims house. Some posters have argued that this was done intentionally as he didn't think anyone would trace the knife to him and that he would be able to talk his way out of it anyway so it was good to leave there as a kind of calling card to further cause pain on the family. Not sure i agree with that though, sounds a bit like clutching at straws. He should have lobbed that thing for miles.