First reports spoke of 12 dead, but 11 people died in the two pile-ups on the Trakia motorway, said Marian Marinov, acting head of the National Investigation Service. More than 50 people were hurt.
An earlier BurgasMedia report on the investigators taking over the case was based on the first figures.
See also: National Investigation Service takes over case of Trakia crashes with 11 dead
The acting chief prosecutor gave the case to the National Investigation Service after the supervising prosecutor asked him to. Prosecutors call the case especially complex, in both fact and law, and say it needs investigators with high skills and experience in similar cases.
The Interior Ministry's regional directorate in Yambol opened the pre-trial proceedings. The district prosecutor's office in Yambol leads the inquiry into the causes and oversees the case. The appeals prosecutor's office in Burgas is giving the investigators more extensive guidance.
Ten investigators and three forensic officers with a mobile forensic laboratory are working at the scene. They have already examined the site and questioned witnesses. Questioning continues, as does a second inspection using a drone.
Investigators will question about 100 people, including police officers and firefighters.
There are 51 forensic medical examinations. Some are on the dead and will establish the exact cause of death. Those for the injured are still to come. After the drone inspection, an automotive technical expert report on the cause of the crashes will be ordered. Valuation experts will then set the size of the property damage.
The statements of the driver of a Romanian lorry are being checked. In his first account, he says he slowed to 50 km/h because a broken-down car was ahead of him.