Since no one has really taken the time to thoroughly debunk this yet here you go:
Theory 1: The first thing the video tries to allege is that there is a second shooter. They love to grab early media footage and then use that as "evidence" of their claims, as if the media's first reporting is somehow golden. Odd that conspiracy theorists distrust the media, then turn around and use its raw reporting claims as evidence. Anyway, you can easily google and figure out who the guy in the woods was.
https://www.youtube.com/watch?feature=player_embedded&v=Y6C2YmOLWnM[1]
He is the father of a student there and the athletic director at the highschool. He was on his way to the school to help make gingerbread houses with 1st graders when he heard the shots. He was unarmed, arrested, detained, questioned, and let go. The story of the guy in the woods was a dead end, so the media dropped it. That is the problem with the 24 hour news cycle, they will report any lead they get before sorting out facts. However, this is hardly evidence of a conspiracy.
The video even makes the ridiculous claim that since the guy was sitting in the FRONT of the police car, that he must have some "crazy" credentials. Yeah, what is more likely...that this guy was a concerned father or that he was a man with some "crazy" credentials on a black ops mission to shoot up a school but he just didn't have the skills to properly vacate, and so he ended up getting himself captured by lowly local law enforcement, AND broadcast on national tv, potentially exposing his super secret black op? C'mon.
Theory 2: The gun discrepancy. This can be chalked up to contradictory reporting, which is going to happen when the media competes with itself to be the first one to break any new details. There have already been articles discussing these discrepancies. What is known for sure is he carried at least 2 handguns into the school and had a shotgun in his car. The discrepancies come in when talking about the other weapons, some sources claim it was a Bushmaster AR-15[2] , others claim it was 2 additional pistols[3] and the AR was left in the trunk with the shotgun. Recent reports have concluded that the shooter did in fact carry 2 pistols and a Bushmaster AR-15 into the school with him. The video just merges all of these conflicting reports to say how the story doesn't make sense. This isn't evidence of a conspiracy, just terrible reporting and fact checking.
Update: The State Police released a new report today January 22nd, 2013 (over a month after the shooting and a week after my post)...to clear up confusion around the conflicting reports. source[4]
Police released a news release on Tuesday, saying they provided details in news conferences but wanted to eliminate any confusion or misinformation.
Police said they found a Bushmaster .223 caliber model XM15-E2S rifle with high capacity 30 round clips, a Glock 10-mm handgun and a Sig-Sauer P226 9mm handgun inside the school.
Police identified Adam Lanza as the gunman who shot and killed 20 first graders and six staff members.
Police also searched Lanza