Ok some Facts - and you don't have to go into any assumptions about why.
They never found JB footprints in any blood
They never found any forensic evidence of his exit from the house
There was never any clothes /gloves found hidden or burnt
No one saw him go to WHF or leave the house and arrive back home
They never found any fibre from the gloves he was supposed to have been wearing
They never found any physical evidence of a fight on him ( or Sheila for that matter)
They never found ay blood or evidence of him disposing of evidence in his house ( where the police were the next day)
No one saw him disposing of any evidence ( despite the family watching him like a hawk)
There was no evidence on the bike or his car or the wetsuit 
No evidence not even one tiny bit was found on any clothes or shoes of blood from any of the victims.
So therefore you think he would have been one of the most meticulous and clever murderers - but no he then apparently told his girlfriend who he was about to break up with.
And don't bore me with the old story he had a month to dispose of everything - unless he was psychic and knew the police were like the keystone cops he did not have a month - it is one of the most stupid arguments I have heard on here . Plus according to some he was too busy galavanting around to have time to be scrubbing the bike with bleach 
Police didn't search for fibers so how would they find any? In any event unless you have somethign to match a fiber to they are worthless.
The killer clearly wore gloves and had blood on his clothing. Plenty of blood woudl have gotten on the killer while beating Nevill- more than enough for such blood to give away he had beat Nevill severely with the rifle.
Sheila had reason to use gloves or change after murdering everyone and would have had no opportunity to conceal such gloves or clothing which you admit wasn't found at WHF.
Jeremy did indeed have a month to dispose of evidence but he didn't need tha tmonth. He had the opportunity to dispose of the evidence after leaving WHF before ever calling police. Since he called police he had all the time he wanted to wash, change and dispose of evidence.
So let's compare- Sheila no motive to change her clothing and wash up and no opportunity to get rid of such so that they would not be found but Jeremy had motive and opportunity.
Closing your eyes to the evidence doesn't make it go away.