Whether or not to secure (by locking) vehicles, apparatus, and compartment doors while outside (and sometimes inside) the fire station has always been a topic of debate in departments where I've worked through the years.
In some places the idea was unthinkable ("it will slow us down"); in others, it was the order of the day if you wanted to ensure things stayed in place while away from the rig.
I remember a big push to secure fire and emergency services vehicles (and other items) after the 9/11 tragedy, in a concern that terrorists would steal them and launch attacks using the implicit trust that rolls along with fire engines, ladder trucks, and ambulances.
This unfortunate event in South Carolina, while rare, certainly suggests that vehicle security, even on incident scenes, is still something to consider.
I'm not sure what the right answer is, especially given the limited staffing faced by most fire departments.
Are we supposed to keep someone in the cab all the time? That's fine (and probably a good idea) in the grocery store parking lot, but what about during a vehicle extrication where the driver/operator needs to move around the vehicle?
It's a fact that locking the (passenger and/or compartment) doors will slow us down, but I guess we need to balance that against the potential that someone with nefarious purposes will hijack our vehicles and equipment.
What do you think?