The wind is flowing from the west, which means the fire will catch up faster towards the east than towards north or south. Newton can choose to go in either directions (north or south). Also, we can assume the fire will consume larger areas in the directions of north and south as it moves further towards the east (i.e. making a frustum-like fire zone). Hence, after reaching south (or north), Newton can choose to move towards the extreme southern west (or northern west) in due time.

While I was keeping the old stuff in the room, the murderer must have carefully replaced the original lock with another one whose key he owns (of course, the other lock looks like the original one and also follows the same locking mechanism i.e closes without the key but opens with a key). So, while locking back, I  closed the lock without knowing that the original lock has been replaced. Once the murderer puts the dead body inside the store room later, he puts back the original lock and closes it. Hence, it seems as if I have put the dead body inside.