Where did my catfish go???!?

I had a small catfish in a ten gallon tank with a black moor and another goldfish. I noticed that the cat fish suddenly disappeared from the tank one day. I cleaned the tank and searched for him but found no trace of him. Where did he go??? About two days later the black moor started to change color and died the next morning. Everyone I've asked said he must of ate the catfish or that the catfish jumped out the tank. I looked but did not find any sign of his body around the tank. The only other things in the tank were the filter, a cave mountain ornament (which I've checked inside and out), and rocks at the bottom. I also don't see how either gold fish could have eaten the catfish since their both not that big.