Security cameras filmed a suicide bomber as he drove a truck laden with explosives at an Istanbul synagogue, Turkey's interior minister said.
Six Jews died - most of the other victims were Muslim Turks
The footage is not clear but police are trying to identify him, Abdulkadir Aksu told a Turkish newspaper.
Turkey's cabinet is holding talks about the two synagogue attacks that killed 23 people and wounded 300 on Saturday.
The meeting takes place hours after claims surfaced saying the blasts were carried out by the al-Qaeda network.
The London-based Arabic newspaper al-Quds on Sunday said it had received a statement from al-Qaeda in an email.
It said the group targeted the synagogues because Israeli agents were working there, al-Quds editor Abdel-Bari Atwan told the BBC.
Turkish Prime Minister Recep Tayyip Erdogan, who is meeting senior ministers, said: "Our security teams, our intelligence services have to work to determine the extent of truth of the claims."
Interior Minister Abdulkadir Aksu told the Vatan newspaper that the attacks were carried out by two suicide bombers who detonated explosives as they drove past the Neve Shalom and Beth Israel synagogues.
Neve Shalom's security cameras caught one of the attackers moments before the blast, he said.
"He is in the footage, although it is not clear. We are trying to establish their identities... It is also not clear whether they were Turkish citizens or foreigners."
The Turkish authorities have also said that closed-circuit television at each synagogue filmed the licence plates of both vehicles. Their owners have been traced and are being questioned, although they have denied any involvement in the attacks.
Turkish officials have largely discounted an initial claim by a local fundamentalist group called the Islamic Front of Raiders of the Great Orient and believe instead that a major foreign organisation was responsible.
"There is no organisation in Turkey that could have carried this out by itself. It's obvious the planning was done with a foreign source," Mr Aksu was quoted as saying.
Police hope if they can identify the suicide bombers they can follow up leads and find out which group was involved.
Hard to check
On Sunday Mr Atwan told the Arabic satellite TV channel al-Jazeera that the statement was from an al-Qaeda division called Brigades of the Martyr Abu Hafz al-Masri.
That division had claimed responsibility for the attack on the United Nations headquarters in Baghdad - which killed 23 people in August.
Analysts say it may be impossible independently to confirm that the latest statement comes from al-Qaeda.
The bombs, which went off minutes apart outside synagogues in the districts of Beyoglu and Sisli badly damaged both buildings and scattered wreckage over a wide area.
Most of those killed in the attacks were Muslim Turks, who lived, worked or were passing by the synagogues when the explosions occurred.
Six Jews were also among the dead.