In my area, it is usually raccoons. (But I am right at the very edge of the otter distribution.)
Mine usually leave foot prints in the mud where they caught or washed their meal.
Much easier to get on the game cam if they have a favorite spot. If they go all around the pond then you will just have to get lucky eventually you should get them on camera!
I expect the little thieves will be wearing black masks to hide their identities.
