A Turkish court has sentenced five people to life in prison over the assassination of the Russian ambassador to Ankara more than four years ago, state media reported on March 9.

Ambassador Andrei Karlov was shot dead by an off-duty police officer at the opening of a photography exhibition in the Turkish capital in December 2016. The 22-year-old gunman, Mevlut Mert Altintas, was killed by police shortly after the diplomat was slain.

In 2018, Turkish authorities indicted 28 people for involvement in the crime. They have alleged that the gunman belonged to a network led by a U.S.-based Muslim cleric named Fethullah Gulen.

Ankara has also accused Gulen’s movement of masterminding a failed coup earlier in 2016 — which the cleric denies.

Turkey has repeatedly sought Gulen’s extradition from the United States, but Washington has resisted the pleas.

Based on reporting by Reuters, AFP, and Anadolu