I don't know about them being hired for this job but it would be reasonable to assume that they might have been put up to this.. Too many loose ends otherwise. The accused have been in jail for a reasonably long period of time & now suddenly they hated Sarabjit ? Bricks & sticks are not probably handed out to prisoners on a daily basis, I assume.
In any case, this is now water under the bridge. I don't have much respect for those celebrating a death cause in this manner but what the heck, that is hardly the end of the world. Good for Sarabjit Singh anyway, better to have died than to spend the rest of his days as a vegetable in a hostile country.