The unsolved mystery

It happened last Monday around 12 midnight. I was watching tv and suddenly i heard a weird noise came from the fish pond area. It was really strange and scary because it was loud. The sound was like a 'living things' struggle on the pebbles bed. No sound from the 'thing' only the sound of scratching and struggling that came into contact with the stones pebbles area. And there was a few times a sound of water splashing or something going into the water. I had a bad feeling on it, so I sneak a peek at the door to see it, but I saw nothing. Plus I was scared that I didn't want to see anything bad so I closed the door immediately. I rushed and just went to bed.

On the next day, I done my routine feeding the fish. I closed the water system for a while. At first, I didn't realise anything until a few hours later when saw the foods a gave didn't finish like usual. I wonder why, because it is really unusual for them behaving to not eating. Then I realised that there was only 2 fishes in the pond with a tortoise! Where are the rest?! Then only I realise the 2 fishes corpse lying on the stones pebbles bed. The big Patin fish In which have been beaten by something. And the other is the small kaloi fish. I think the rest have been eaten by the 'thing'. I wonder what the thing is. It can't be fish because the bites is big for a cat. Nor can't be a dog. Dog can't climb a fence. Then, what is it??