I think the cops took the bodies over before the shooter arrived. That's why they were already parked at the funeral home before he even wrecked his vehicle (the excuse was because his grandma dialed 911). They wouldn't want it seen in broad daylight. They likely carried the bodies over before school started when cameras were like messed with or taped over.

Students were doubled up and not allowed into that building. The crime scene was prepared that morning. I suspect the bodies were put in a nearby room and brought out after the shooter was neutralized. They would want the to have time to warm up to room temperature.