There was a piece of light blue cloth, but considering how Hydra's side of the garden was uneffected--cleanly so, the thief side of my brain is screaming "Set Up". Of course, that doesn't clear Delphinus completely, but I think Black talked with them a bit about it. No confirmation.
Then there's always a chance it's Canis. But let's be logical here. Even if Chika--Gray, that is--and Lightning have their problems, Canis is not the type to take personal matters and make them into team matters. Jace wouldn't allow it, for one, if he found out about it.
There's also the possibility of it being Lepus. But that seems not quite right because Mao would have gloated about it, laughing and making a big noise over it. Let's face it--Lepus is too heavy handed for this to be their work.
Those would be the three main suspects... however, I have reason to suspect another party. I have no evidence to back it up, however. And that's the delimma I'm facing.