For the lawyers who on Saturday filed a suit seeking to hold Syrian President Bashar al-Assad’s regime responsible for the death of veteran war correspondent Marie Colvin, the work was intensely personal.

Colvin’s sister, Cathleen, a former Shearman & Sterling associate, is a plaintiff in the wrongful murder case brought under a little-known law. The Foreign Sovereign Immunities Act lets victims or their families sue designated state-sponsors of terrorism for the murder of U.S. citizens.