It's a plausible enough theory, but would an older brother become so extremely impaired and mentally ill that he'd be able to subject his wee sister, his own flesh and blood, to such a prolonged sanguinary fatal attack? Remember, this was a physical assault of unalloyed ferocity and savagery. There didn't seem to be any signs of any disharmony in the Jones household just before Jodi set off to meet LM at 1650; on the contrary, it seemed all was peaceful and calm -- Jodi, Joseph and Judith all sitting together in the living room listening to a Rod Stewart record (but, then again, would Judith have let on if there were any arguments between them at that point?). Besides, it's standard practice and procedure for the police to take DNA samples from the immediate family of the deceased in a murder investigation -- nothing incriminating was found. As for the 5 unidentified DNA profiles -- 1 of those was JAMF and 2 were from a couple of vagrants living in a cave nearby. As for the remaining 2, well, we'd need to see what the source was (eg, semen, blood, saliva, skin, nail, hair), if they were full profiles or partials and the electropherograms. I suspect they were from semen, so, as Jodi was not sexually assaulted, those remaining 2 profiles got there innocently. Even if they weren't from semen, I strongly suspect they still got there innocently.
Were the vagrants found and dna tested?
As for it being harmonious in the jones house hold, how do we know that? We can only go by what they told us. If the theory was correct and it was the brother that did it, the family is hardly likely to say it was all kicking off when Jodi left, with her brother hot on her heels, are they?
Putting the 2 circumstantial cases against each other the case against the brother seems strong too. Couple of examples
Possible sighting of Luke and Jodi top of path
2 possibly sightings of [Name removed] and being closely followed by her brother wearing a back pack
Luke know to have small/medium knives
[Name removed] bother known to have big large knife carried in a back pack
Luke possibly threatened girl with knife, but not known to be violent
[Name removed] brother known to be violent and attacked [Name removed] in the weeks prior to murder
Luke teacher said something about his possible mental health, can’t remember what but psychology reports said he had no mental health issues
[Name removed] brother had serious mental health issues making him a danger to others if medication not given, he was off his meds at time of murder
Luke found the body
[Name removed] own brother did not even go out to look for her, his grandmother and sister did, they wanted to search the path even though luke had just come that way.
Possible sighting of Luke at foot of path
Missing parka that was not proven existed in the first place other than word of mouth.
Accused of burning cloths but again no evidence
Alibi was making dinner. Confirmed by mother, brother could not remember
Main witness did not identify him in court
[Name removed] brother cannabis known to make him have psychotic episodes, had a huge about the afternoon before the murder.
Appointment with mental health person cancelled that afternoon
Previously stabbed his mother and attacked other members of the family
Alibi was in his room all night, nobody seen him but they knew he was there.