What do you think the DA bases their investigation on?
It's based on witness statements and the deputy's statement obtained by OCSD investigators.
You do not know this?
“What do you think the DA bases their investigation on?”
They have their own investigators, sworn LE, detectives, called “DA Investigators”. They work for the DA. Not the sheriff.
I have no doubt that they have a very detailed policy manual on who, exactly, interviews witnesses after an OIS. Since they’ve gone to the trouble to set up an outside office for all OIS’s, it seems reasonable that they would have that office conduct the entire investigation, not just some small bits of it.