How did my larva die?

I've had a death toll of 4 Axolotl larvae in the past 2 days, and the most recent one gone, snapped into 2 pieces when I put him down the toilet.

His tail was curled, just like his his sibling's (who died a quick death). I put him into my 'sick bay' for a few hours, and he was just twitching in his last minutes of life. I checked him, and he had definitely died.

I put him into the toilet, and watched as he snapped into 2 pieces! Now I regret not culling him, he must have been in alot of pain.

But the question is, why, and HOW did he die? This hasn't happened to the other deceased larvae

Irrelevant Information:
The thing i'm hoping for is that my favourite Golden Albino, my leucistic and a wild type make it. I might keep my Golden Albino and the leucistic, because the golden I like has eyes that seem to sparkle, and my mum loves him I also have a definite leucistic larva, because his underside and half of his sides are white, and some of his back is white.

Their front leg buds have also dissapeared from view, and i've noticed 4 little finger looking things off the biggest, who looks like a wild type, but could be leucistic.

The mother is a leucistic with blue eyes, and the father is an olive wild type.

Well, most likely the reason it snapped in half was because it was dead, not necessarily how it died. Dead animals usually get really stiff when they die and it's easy to break bones.