Still probably too early to know for sure, but yeah, what I've noticed of chatter suggests the motivation was due to the ties in question, after the moonies fleeced his mother for a great deal of her personal wealth.
And, like. Shit actually kinda' hits close to home? My grandmother has been defrauded of several thousands of dollars (probably breaking 10, but the records are spotty at this point) over the years by similar exploitation of the elderly (and they're not exactly a rich household -- relatively well off for our area, but it's an amount that would have gone a long way towards making their home more livable or providing for end-of-life care that's now being struggled with), with exactly fuckall remedy provided by legal avenues. I can viscerally understand the urge to see someone connected to the fucks that have done that to a loved one put in the dirt. Not something I'd do myself, I don't think, but, like. If that's actually what pushed the guy that far, I understand it on a very personal level.
The anger and frustration involved when someone's viciously exploiting a loved one and you can't get it to stop or otherwise receive some kind of remedy for the abuse... it's an incredibly genuine one, and one I can easily see pushing a person to kill. The hardest part of it is usually actually finding a target, and, well. Abe was public, visible, and accessible.