Police say investigations indicate the driver of a bus that crashed Sunday, killing 13 exchange students, may have fallen asleep or become distracted moments before the tragedy occurred in northeastern Spain.

Regional police commissioner Miquel Esquius told reporters Wednesday that although investigations are continuing, police believe the driver may have dozed off or become distracted by a mobile phone or by talking to someone.

He said many of the nearly 60 students on the bus, including the 13 who died, were not wearing seat belts at the time of the crash early Sunday.

Seven of those killed were from Italy. The other six were two Germans, an Austrian, a French woman, a Romanian and an Uzbek.

The driver is one of 19 people still being treated in local hospitals.