Goofs

They didn't even make an attempt to make the arrow look like it penetrated Oscar's body enough to do any serious damage. The point of the arrow can be seen to be stuck in something under Oscar's shirt having only penetrated just enough to knot fall out.

Oscar sits facing Malcom's desk when he is hit by an arrow that comes from the direction of Malcoms desk. There is a wall with a closed window behind Malcom's desk. After Oscar is hit by the arrow Malcom opens the unbroken window and climbs outside to search for the killer. It's never explained where the arrow could have come from.