When Salem makes his second escape, at night after lights out, all scenes outdoors until he returns to his cell and pretends to sleep are obviously daylight. No attempt has been made to use a day-for-night filter.
When Salem is swinging on the rope and climbing down the tree, it's an obvious double with a stockier build and darker hair.
The killer, Salem, is eventually, at the end of the film, proven to have been out of the asylum by the parrot in his clothing. However, this and each earlier time he was out could have been easily identified by his boots, which would have been soaked by the snow that he had to trek through.
At the beginning of the movie, when Salem is outside running around in the cold all that time, you never see his breath. Obviously, it wasn't very cold when they shot it.
The police never see the many footprints Salem left in the snow.
When Salem is returning to his cell, the second time, just before he locks the door.
When the Inspector and Doctor are exiting Salem's cell.