Two more band-aids:
After Wolfy locked Wulfy in the ferris wheel, while Wolfy was on his way to the control panel, Lykos or Lupa ran up, unlocked the cabin, and ran away. (Wulfy probably asked them to do so beforehand. Helping the victim doesn't make them an accomplice.) Once at the top, Wulfy could then escape using the cabin as stairs, or with a rope or bungee or something. The culprit ambushed Wulfy when he reached the bottom, I guess.
The culprit got into the apartment by breaking the window and replacing the glass.
Let's patch up DWaM's theory. Might as well take the madness as far as we can get it.
The culprit picked Wolfy's pocket, taking the key and the charm. Probably in the morning, on Wolfy's way to work, before he was too far away from the apartment. The culprit then at some point un-picked the key back onto Wolfy's person. (Could've been shortly before Wolfy returned home; the culprit could have returned the key, then rushed ahead back to the apartment building, entered through the window they had left unlocked, and locked it by hand.)
The Ferris Wheel escape is the same... except instead of just jumping off from the top, they climbed to the top of the cabin that Wulfy had been in, went halfway down the Ferris wheel but using the tops of the cabins as stairs, and then jumped into the river. (I guess you could go the full way down that way, if you're lame.)
Even if the culprit isn't an evil leprechaun, they can bypass the camera easily by leaving the incapacitated Wulfy outside of Wolfy's apartment window, entering the front door, and then pulling in Wulfy's body through the apartment window.
Once the crime scene was set up, the culprit locked the room from the inside, affixed himself to the ceiling right above the door, and then maneuvered himself out while Wolfy and Neuro were distracted by the corpse, before the search of the room occurred.