That would explain why the police spent so much time searching the HD parking lot, and left the school parking opposite Rt 50 alone for 36 hours (in fact the newsies used it to park their trucks, and the police seemed entirely disinterested in declaring it a crime scene, at least for the first day-and-a-half).
But on the other hand it doesn't explain why the police later declared parts of the school grounds as a crime scene, and began searching the parking lot on Wednesday morning.
Either the shooter was near (or in) the HD parking lot, or the shooter was near (or in) the school parking lot. Not both.
So I'd guess there is some uncertainty in the account you've posted. Otherwise they'd never have spent time at the school grounds, even if it was 36 hours later.