The police searched the car just before entering the school. A mother is interviewed here and tells of seeing the doors of the vehicle opened and things strewn about outside the car. I’m sure that search included the trunk where they found the shotgun.
http://www.youtube.com/watch?v=ptbd6qRY358
AGAIN, there is nothing that says that car was searched.
There were items that look like clergy outfits outside of the car.
Open doors does not mean the police searched it. The items were not close to the car like they had just been thrown out during a search.
Ryan could have left the doors open
Yes, I have seen that video and I believe the police probably did search the car before or shortly after entering the school. However, it seems that they should have secured the weapon at the time they found it and not hours later. Perhaps they did not search the trunk at the time of their arrival on the scene, and that oversight did not occur to them later.