That's all of them, lexxy; there are five Mystery Trackers games so far.
If you like Elephant Games and the fact that they are more like adventure games with a few hidden object scenes thrown in, I can recommend these other games of theirs as well:
Hallowed Legends: Ship of Bones
Surface: Mystery of Another World
Grim Tales: The Stone Queen
Grim Tales: The Wishes
Surface: The Noise She Couldn't Make
Surface: The Soaring City
Christmas Stories: Nutcracker
Urban Legends: The Maze
And there are others....those are just a random sampling.