You can not prevent a random killing or two. It's not possible even if you bring down a chinese level surveillance infra onto Kashmir.
Pakistan doesn't need to support terrorists for such a murder. It is a really simple thing to do, and I doubt it involved any Pakistani handler anyways. If it did, Kashmiri terrorists are the most incompetent terrorists to have ever existed.
ISI has various factions within itself and one faction may refuse to support the terrorists but another never will and it becomes a hodge podge of an intel op to find which faction is doing what.
On the likely chance that ISI goes defunct (what with the current economic beauty), JeM and LeT will buy/borrow weapons from any of the hundred terror groups and stalls in Darra and a single consignment getting across the border will mean multiple murders.
This will not stop. You can do everything you want.
You want to fix this, you'll have to fight this down on a societal and communal level and it will still present a spurt in killings before it stops altogether. This is a matter of a couple of decades, at least.
As sad as it is, it should be a relief to everyone that the "freedom fighters" who were supposedly going to "liberate" Kashmir are now conducting ops that Bihari chapri boyfriends do for "meri ladki ko line maar raha tha".
See, I'm as angry as you regarding Kashmir but the matter of the fact is the logistics behind a random murder of some guy going to a grocery store is just too simple and too hard to track. There's no personal motive, there's no telegraph as to who the next target is going to be, there's no pattern. It's nigh impossible to prevent or pay back in kind unless the government decides to go full african warlord.