Plan A: A Scenario

After dispelling the notion of Plan B with the fact that the gunmen at Columbine repeatedly said the library was going to explode with them inside of it, meaning it was never true that they "started shooting when the bombs failed", one is required to replace it with a better theory, a theory which says plan A was very much in play when they began shooting, meaning they never planned to shoot from the cars.

One also when challenging any theory is faced with  the burden of replacing it with a better theory. I submit I have one, and feel it must be true in essentials, while I confess knowing everything they planned that day is probably impossible.

As best I can tell, here was their plan that day.

When the first cafeteria bomb goes off, they are shielded from the blast up on the stairs. Dylan was then to descend the stairs and shoot fleeing students with his TEC-9. Eric was to stay at the top of the stairs and shoot police with his carbine, covering Dylan's back. Eventually, those fleeing the cafeteria learn to flee into the parking lot is to be shot at, and turn around to run up the cafeteria stairs. When this happens, Dylan is to run back up the stairs, and Eric and Dylan will enter the west entrance and cut off their escape. All the while, they also have pipe bombs and crickets and Molotov cocktails to toss to kill, confuse, and cause fires, as well as just general carnage of more exploding corpses.

They would have spent some ammo and been much closer to people, so maybe this is where they use their knives as well as shoot. The second bomb goes off at 11:35. Perhaps it was simply a back up. Perhaps it was estimated 15 minutes until victims turned around, or maybe by then it would be killing those who have turned around a second time, realizing now to run up the cafeteria stairs is to die, as well as perhaps kill Eric and Dylan. Also perhaps any firefighters or police or paramedics who run into the cafeteria to help after the bomb.

One of the car bombs goes off at noon, and another probably some time after. Most likely to kill first responders and media and what is left of the students on live television. Maybe Dylan's is for the responders and media, being more or less across from the center of the cafeteria, and Eric's is for the students evacuating the school, being by the south entrance.  Maybe Dylan's was to explode first causing victims to retreat to where Eric's car would again explode.

This is why they chose the stairs. This is why Dylan did descend the stairs, and why he shot only 3 times with the TEC-9 before that, but spent the shotgun into Lance.  Dylan also relished the library massacre more, entered the library first, said he had always wanted to do this, was more vocal in general in the library. Indeed he wrote about going on a killing spree first, and was the first to write about going "NBK" (their code for the massacre, from the film Natural Born Killers). He had been suicidal for years at this point, and seemed to want others to feel his pain, his "Wrath" as his shirt said.

This is why Eric stayed up there. He could not see people fleeing out into the parking lot from his vantage point, and the only cafeteria exit he could fire at left the possibility of injuring Dylan, and they would probably be deterred from that one by Dylan's presence anyway. Eric and not Dylan was also the one to shoot at police that day. Eric also dreamed of putting everybody in a Doom game where they had to shoot at monsters shooting back at them, of "Natural Selection" as his shirt said.

This is why when Dylan enters the cafeteria from outside, and sees the bomb has not exploded and people are running up the stairs. He only smirks and turns around to tell Eric, and they then enter the west entrance.

This is why Rachel and Richard are shot first, blocking access to the west entrance, and Daniel and Lance and Sean shot next, for blocking Dylan's path down the stairs.

They did not use their knives, so many will say they were for show. But tying it to your ankle does not seem the best place "for show", and both and especially Dylan (who mentioned using his knife in the library) were interested in Charles Manson, who of course influenced a series of stabbings. Also, on the Basement Tapes, they both mention using their knives. It seems to me a theory incorporating use of the knives is better than one that doesn't. They could have also just been a contingency if anybody tackled them or some such.