French authorities have opened a terrorism probe into the sister of a radical Islamist who committed a 2012 killing spree in southwest France.

Scores of police, some wearing masks, on Thursday raided the home of the sister, Souad Merah, in the southwest city of Toulouse, but she was not at home. The Paris prosecutor’s office said she faces a preliminary investigation for suspected association with a terrorist enterprise.

An Interior Ministry official said French authorities believe Merah has fled to Syria with her young children. The official spoke on condition of anonymity because he was not authorized to disclose the information.

In three separate 2012 attacks, Merah’s brother Mohammed shot dead a rabbi, three Jewish children and three paratroopers in southwest France before dying in a shootout with police. French authorities say Merah was of Algerian background and had traveled to jihadist training camps along the Afghanistan-Pakistan border.

Souad Merah’s mother, Zoulikha Aziri, told BFM television that her daughter had traveled to Tunisia on vacation with her husband, not to Syria.

French officials have expressed fears that hundreds of its Muslim citizens who have traveled to Syria in recent years could return home from the civil war there could return to France and commit terror attacks. They say France has more of its young people joining the fight against Syrian President Bashar Assad’s regime than any other European nation.

(AP)