I think it would be pretty easy to look at all the empty bullet casings on the floor of the school and determine whether they were pistol or rifle rounds.
I listened intently to the news that day and they were earliest reported as being rifle rounds.
The reason I remember is that the next report said they found pistols with him and I thought Huh??
The first report of a rifle said they found it in the trunk.
And I thought Huh? again.