Patti and Brian were shot first

On the orthodox story, Rachel Scott and Richard Castaldo were first to be shot. Several more were shot (Daniel Rohrbough, Lance Kirklin, Sean Graves on or near the stairs, Michael Johnson and Mark Taylor in the grass, and Anne Marie Hochhalter) before Klebold descends the stairs and enters the cafeteria, then goes back up the stairs. Then Patti and Brian are shot at the west entrance.

However, Patti notices Harris is wearing his trench coat and something on his head. But Harris ditched his trench coat after shooting Rachel and Richard, and if he wore the balaclava at all, it was only at the beginning.  We have a contradiction to reconcile.

It is easy to do so. Patti says it was around 11:20, which would fit being shot first. Strongest of all, Bree Pasquale, the most perceptive witness, very clearly says Patti ran into the library, then she looked out the window to see Klebold toss a dud of a pipe bomb into the parking lot, which is exactly what Richard describes happening before he was shot, then she witnesses the victims on or near the stairs shot.

This means there were 4 victims shot at near the west entrance to begin the massacre. Very clearly, the first priority was to clear the west entrance, and most likely because when the victims turned around and rap up the cafeteria stairs, after being shot for fleeing into the parking lot, Harris and Klebold would cut off their escape by utilizing the west entrance, which is exactly what they did.

It also means all the speculation about why poor Rachel was shot first, whether it was because they hated Christians, or because Klebold had a crush on her, has a false presupposition - she was not shot first. It also makes a bit of sense for an authority figure like a teacher to be the first target.