Seher Cagla Demir, a woman born in 1992 in the eastern province of Kars, has been identified as the suicide car bomber behind the attack in Ankara, according to a written statement from the Turkish interior ministry.
She is believed to have received training from the Syria based Kurdish rebels known as the YPG, according to the statement.
Demir was in Syria by December 6, 2013, after traveling to the city of Diyarbakir in the predominantly Kurdish southeast on November 30, 2013, according to the security source. Her family, who still live in Balikesir where Demir attended university, reported her missing on December 5, 2013. Balikesir is in western Turkey.
Although Turkish officials have not provided further information on her movements after her disappearance, they are convinced she joined the ranks of the Kurdish armed group the YPG in Syria.
"The attacker has been a part of the separatist terrorist organization PKK and later crossed into Syria and received terror training from the terrorist group the YPG," said a written statement released by the interior ministry. The Turkish security source characterized it as "weapons training from the YPG."
Ally or foe? Turkey and U.S. don't agree
Turkey and the United States consider the PKK to be a terrorist organization, but the two NATO allies have been at loggerheads over the classification of the Syria-based YPG. While Turkey views the group as an extension of the PKK and therefore a terrorist organization, the United States sees the group as one of its most reliable and effective allies in the fight against ISIS in Syria. From time to time, Turkish artillery have fired across the border at YPG positions in Syria.
So far, no one has claimed responsibility for the suicide car bomb that detonated in Ankara's bustling Kizilay Square.
In February a PKK offshoot known by the acronym TAK claimed a previous bombing just a few hundred meters away that killed 30 people. In that bombing, the government released the identity of the attacker as a Turkish citizen who also traveled to Syria and apparently re-entered the country posing as a Kurdish Syrian refugee.
After the bombing on Sunday, the Turkish military hit targets in Northern Iraq in the Qandil Mountains where the PKK maintains a presence.
Security forces and the PKK have been fighting in provinces in southeastern Turkey since a ceasefire fell apart over the summer.
Some towns have been under curfew with military operations to clear out what the government calls terrorists. But critics argue the heavy handed operations are collective punishment and security forces have been acting with impunity killing civilians.