"They did it"

I can almost always tell when Jaelyn is telling lies. Her twinkling eyes and smile give her away. With Allie and Caden, I cannot normally tell. Tonight, I went to the basement to get them started on cleaning up and discovered that someone had played in the kitty litter pan (gross) and I haven't cleaned it out today (double gross). There was kitty litter all over the floor. I questioned all three kids and cannot figure out who did it. Jaelyn says Allie and Caden did it. Allie says Jaelyn and Caden did it. Caden says Allie and Jaelyn did it. Who to believe? Could they have all been in on it? I cannot tell from any of their faces who was telling the truth. They all lost tickets since no one would fess up to the crime. Why in the world would a child want to play in kitty litter? I've talked over and over with them about her the kitty litter pan is the kitty's potty. They don't play in the big potty. Ewwww!