Found My Missing CPD!

Initially I bought six ember tetra and six celestial pearl danio for my aquanano 40 and was going to let them settle in before getting more fish.
Quite soon afterwards there were only five CPD, they move about all the time, and love to hide in the plants but I was pretty certain that one was missing.
The other day I found half a fish (probably an ember tetra but hard to tell as it'd gone a bit grey) suspended in some plants. I counted, and yes, I was down to five ember tetra.
So two fish down, but only half a body!
Today (bearing in mind I bought the fish about six weeks ago, and CPD disappeared soon afterwards) my son handed me something small and flat. A dried out fish! It was perfectly preserved except for a missing tail. My missing CPD. I asked my son where he found it.
"A burglar came into the house and took a fish and put it on the sofa"
(He's five)
So no idea what happened. There is a very small slit down the sides of the aquanano glass lid, could it have jumped out? Then been found and hidden somewhere by the kids.
It's not a newly deceased fish, as at first I was worried it might be. So I spent about half an hour intensely watching the tank, counting three fish, four fish, three fish again, and eventually saw five CPD in there, phew! They really do like to hide!

Yes, I suppose the gap is wider than the fish. Weird how they never seem to go anywhere near the surface of the water, even when I'm feeding them.