Based on cellular damage, everything had been killed by something along the lines of a gamma ray burst. Basically a huge surge of radiation, more than enough to kill instantly. I knew that because not only had the animals been killed but their intestinal flora (or the local equivalent) had been killed at the same time. There was no bloating, no rotting from the inside out. I had to make some assumptions, using terrestrial analogies, but I was pretty confident that they would be close enough.