I don't know if the door really was kicked in, or if the police knocked it open when they arrived. However, going with the theory that a perp damaged the door, if Dad went to answer the door, cracked it to see who was there, and immediately shut it because of who he saw, the perp could have feared Dad would get a gun, thus quickly had to gain access to the home before Dad could get a gun.
In my head that makes sense. Element of surprise. Waiting to break a window, find another entrance once Dad knew someone was outside would be too risky.