I feel like the Llanowar Elves are saved because the inactive player's effects resolve first but I'm not sure. It also makes it tricky to Murder anything if my opponent has mana as they can pull this trick, save their creature and have me waste my Murder.
FYI: Rules questions are generally handled in our Rules Forum regardless of the format.
Also, note that normally equipping a creature can only be done at sorcery speed (during one of that player's main phases with the stack empty). Some cards let you equip at instant speed but it's not common. Leonin Shikari is the only card that I'm aware of that can do that.
As for your question, Murder will destroy the Llanowar Elves. Your opponent cannot move equipment on your turn unless something allows them to do that.
Robe of Stars can only save the Llanowar Elves if it was already equipped to them when you cast Murder and your opponent then responded and phased it out.