Afghanistan’s highest court has ruled that the police officer convicted of murdering Associated Press photographer Anja Niedringhaus and wounding AP correspondent Kathy Gannon almost one year ago should serve 20 years in prison, according to documents sent to the country’s attorney general on Saturday.

The final sentence for former Afghan police unit commander Naqibullah was reduced from the death penalty recommended by a primary court last year. Twenty years in prison is the maximum jail sentence in Afghanistan, said Zahid Safi, a lawyer for the Associated Press who had been briefed on the decision by the Supreme Court. The Supreme Court ruling upholds an intermediate court’s decision, which was opposed by the Military Attorney General’s office.

Naqibullah, who uses only one name, opened fire on Ms. Niedringhaus and Ms. Gannon without warning on April 4 as the two were covering the first round of the country’s presidential election outside the city of Khost in southeastern Afghanistan.

An award-winning German photographer, Ms. Niedringhaus was renowned for her humane depictions of ordinary life as well as for her coverage of conflict zones from the Balkans to Iraq, Libya and Afghanistan. She died instantly of her wounds at the age of 48. Ms. Gannon, a senior correspondent for Afghanistan and Pakistan with decades of experience in the region, was hit with six bullets that ripped through her left arm, right hand and left shoulder, shattering her shoulder blade. She is recovering from her injuries while undergoing physical therapy in her native Canada.

According to witnesses and court testimony, Ms. Gannon and Ms. Niedringhaus were seated in the back seat of a car parked in a crowd of police and election officials at a police station when Naqibullah walked up to the vehicle, shouted “Allahu Akbar,” and fired on them with a Kalashnikov assault rifle. He surrendered immediately. Witness and official accounts suggested the shooting was not planned.