"We have established there was a person who was a suicide bomber in this attack. This person had a fake driving license from the United States, from the state of Michigan," Interior Minister Tsvetan Tsvetanov told reporters Thursday.
The Sofia News Agency said initial reports indicated a bomb in a suitcase on the bus transporting Israeli tourists from the airport to the nearby town caused the explosion.
The bomber was caught on surveillance footage shortly before the blast, Tsvetanov said.
"He looked like anyone else -- a normal person with Bermuda shorts and a backpack," Tsvetanov said, adding authorities had succeeded in lifting DNA from the bomber's fingerprints and were trying to identify him.
The first batch of Israelis injured in the attack were to return to Israel Thursday, Israel Radio said. The army said 32 of 35 injured Israelis were on board the plane and the other three were hospitalized in Sofia, Israel Radio said.
Israel blamed Iran and Hezbollah for the bombing. Iran's state television called the allegations "ridiculous."