The "no footprints in the snow" is solid evidence. It proves no one entered or left the house AFTER the dusting of snow fell.
However, we don't know what time it was when the dusting of snow occurred. A light dusting can occur in 10 minutes or so. So if the dusting occurred around 2:00 AM it would preclude anyone leaving the house without leaving footprints in the snow since the killing, crimescene staging, ransom note writing, etc., would have taken at least a couple of hours to complete.
But if the dusting of snow hadn't occurred until around 5:00 AM then a person could have left the house sooner than 5:00 AM without leaving footprints, since the snow hadn't yet fallen when he left.
BlueCrab
However, we don't know what time it was when the dusting of snow occurred. A light dusting can occur in 10 minutes or so. So if the dusting occurred around 2:00 AM it would preclude anyone leaving the house without leaving footprints in the snow since the killing, crimescene staging, ransom note writing, etc., would have taken at least a couple of hours to complete.
But if the dusting of snow hadn't occurred until around 5:00 AM then a person could have left the house sooner than 5:00 AM without leaving footprints, since the snow hadn't yet fallen when he left.
BlueCrab