The Maniac is an alter-ego of SpongeBob who he does not realize he is.
The police only make a sketch of him. It looks like the only yellow-colored sketch of SpongeBob seen on the show's logo. His design is very similar to SpongeBob, except he has no pores and no pants or undershirt.
In the episode, SpongeBob, as a hall monitor, tries to track him down, not knowing that he is looking for himself the entire time.
The police may have been referring to the Open Window Maniac, but they said that he was also responsible for car wrecks.