It had everything to do with inheritance....................but NOT an inheritance which could easily have been another 30+ years down the line (I've just seen the irony!!!) In order to gain his inheritance, Jeremy had to be seen to be dedicated to the farm. He wasn't going to receive it UNTIL Nevill's death and unless that death could be bought forward, Jeremy was likely to be well into middle age before it came his way and leading a life he wasn't cut out for. Certainly, he'd probably have received monies from other quarters but he'd still have had to work on the farm before he received the bulk. He believed it was important to have money whilst one was young. He wanted his inheritance NOW.
As I've said many a time,the grannie's days were numbered and JB probably already knew that his mother would see both Sheila and himself alright by contributing a bob or two to them after her death. JB had no enormous debts or anything which unduly worried him about wanting to get his hands on ready cash,so it's a ridiculous notion to repeat that this murder had been an inheritance one.
JB would also have known that having money in that way takes time,as it would have been 4 months+ for probate,therefore it wouldn't have amounted to " ready cash " any more.
He would have also been permanently on edge and it would have shown. The handing over of the keys to the place spelled honesty towards his relatives because he himself was honest and trusting. Would a mass murderer have done the same ? I would very much doubt it. Mass murderers or those intent on inheritance,want the cash,jewellery,goods now ! That's their whole purpose in committing such heinous crimes,they're ruthless and will stop at nothing.
How many 24 year olds in that position in which JB was in with everything he'd wanted and got go on to commit mass murder which included two little children ? Not a lot,if any. It's more the older person who snaps at the thought of losing everything after having built up a business then through some quirk or other find themselves in a hole and some,through pride,will go on to murder their family then commit suicide as a means to end the problem.
If you,or anyone else can show me proof of a 24 year old killing his family for their inheritance then I will admit that it does happen.
Better still,statistics that also show this along with the same for those with mental illnesses.