Twelve people died in two serious pile-up crashes on the Trakia motorway. A vehicle expert examination will be ordered within days, and a road-construction examination next week.
The road-construction examination will check the state of the road surface and the signs and markings on the stretch on the day of the crashes.
The vehicle examination will cover 20 seized vehicles. Several inspections have been carried out at the scene.
So far 50 witnesses have been questioned, and dozens more will be called in.
About 30 forensic medical examinations have already been ordered for the dead and some of the injured. The other injured are still waiting for theirs.