How many maniacs can i place in the game because the maniac attack card says: if no maniacs are in play choose a lone investigator.Place 1 maniac in his space. Can i have more thaan one maniacs in the game?
(I say typically only because there is one very specific set of circumstances that allows two maniacs to appear, though I can't remember exactly what it is at the moment. But basically, the answer to your question is "no".)
If a maniac is already in play, the Maniac Attack keeper action card cannot place a second maniac in play (it will instead heal and teleport the original maniac). Two maniacs cannot be in play due to Maniac Attack.
Note that Clue 1A, which spawns a boss maniac, has no such clause - the boss maniac is in addition to any maniac that is already in play. So if Clue 1A is revealed while one maniac is already in play, you will end up with two maniacs on the board.