Investigators are analysing footage from Road Infrastructure Agency cameras and data on vehicles that passed toll cameras near the crash site on the Trakia motorway. They want to reach drivers who saw the collision but have not yet given statements, said Marian Marinov, acting director of the National Investigation Service.
Twelve people died and dozens were injured in the pile-up on the Burgas-bound carriageway.
Cars that drove the same way and did not stop have been identified. One of them was stopped on the next stretch of road. Marinov said these drivers could be witnesses if they act in good faith. Investigators are also checking dashcam footage, tachograph records and electronic data.
The driver of the first Romanian lorry has been released because there are no grounds to charge him. Marinov said it is clear how the lorry was moving, and that it was driving slowly because of fog.
The first bus behind the lorry hit its rear, Marinov said. He said a series of chaotic and random events followed, and a reconstruction of the crash will show exactly how they unfolded.
The investigation is at an early stage and is looking in several directions. There is no main theory about the cause yet. Technical expert examinations are due.
Investigators are still working out whether the crash on the Burgas-bound carriageway and the one on the Sofia-bound carriageway are directly linked. They are checking whether the first car on the opposite carriageway was hit in the collisions, or got into danger on its own because of the fog. Marinov said the fog was the same on both carriageways and road conditions affected traffic in both directions.
He said the second pile-up may have happened after drivers stopped to help the injured on the other carriageway.