HCA: Hermit Crab Association

So, for some background, my Australian Nereus brutally murdered my Ecuadorian Phorcys by picking him apart after the latter had just molted and switched shells. Don't know why, stress? A dominance thing? Not really sure.

Anyway, today I got a new crab, a purple pincher I named Keto. She's mostly been keeping to herself, she's settled in and has been burrowing since I brought her home (she's doing so as I'm writing this). Nereus did approach her a couple times, but just watched her from the other side of the cork wood she was burrowing behind. Nothing obviously malicious, he was just checking her out, it seems. After maybe 30 seconds, he got bored and went back to his pool.

The thing is, I don't know if I can stand another murder. Will Nereus strike again? How do I prevent crab domestic violence? For tonight, I am putting Nereus in the PetSmart box Keto came in, with some moss and a Mason jar lid full of water, just for the night until I'm awake to supervise them. I've been making sure they have plenty of food and water so they don't fight over it.

What other precautions should I take? Please help!

You could dip both crabs in the fresh water when you put them together, so that nobody smells like an 'outsider'. Be sure you have the correct types and sizes of shells for each. And be sure to feed plenty of animal protein (meat).