my thinking on how it could have went down:
mom and dad both left for work
holly is on her way out the door to take her test with bookbag, lunch bag, purse and perp is ready for her at the door with a knife somehow cuts her enough for blood loss.. tells her to walk with him and she won't get hurt.. walks her into the tree line
meantime brother heard a commotion.. looked out the window to see the man in camo and his sister seemingly walking off normally.. he thinks... hey that is her boyfriend... maybe he is out early hunting turkeys
hour later he leaves the door to go out and sees blood and sister's car still sitting there and calls 911
MOO