The judges ruled Tuesday during a two-hour hearing that followed a three-month police investigation.
Naqibullah, represented by a defense lawyer provided to him by a legal association, argued with the judges before his sentencing, saying at one point that he was "not a normal person." However, judges dismissed his claim after he provided his name, age and the correct date. Naqibullah also denied judges' claims that he once traveled to Pakistan to be trained by extremists, saying he only received medical care while there.
Afghanistan's president must sign off on any execution order. Naqibullah also may appeal within 15 days to a second court and then ultimately to the country's Supreme Court.
Gannon and Niedringhaus traveled to Khost under the protection of Afghan forces and were at a district police headquarters in a village outside the city on April 4 when witnesses say Naqibullah walked up to their hired car, yelled "Allahu Akbar" God is Great and fired on them in the back seat with a Kalashnikov assault rifle. He surrendered immediately after the attack.
Witness and official accounts have suggested the shooting was not planned. While in court Tuesday, Naqibullah did not offer a reason why he opened fire.
Niedringhaus, a 48-year-old award-winning photographer who had covered conflict zones from the Balkans in the 1990s to Iraq, Libya and Afghanistan, died instantly of her wounds. Gannon, a 60-year-old senior correspondent for Afghanistan and Pakistan, suffered three gunshot wounds in the attack. She is still recovering from her injuries.
The two had worked together repeatedly in Afghanistan since the 2001 U.S.-led invasion, covering the conflict from some of the most dangerous hotspots of the Taliban insurgency while focusing on the effect war had on civilians.