MOSCOW — A Ukrainian court sentenced a former security official to life in prison Tuesday for the death of Georgy Gongadze, a journalist whose mysterious death in 2002 provoked an international outcry and helped set off protests against the president at the time, Leonid D. Kuchma.

The former security official, General Oleksei Pukach, who once headed a surveillance department for Ukraine’s Interior Ministry, testified that he had not intended to kill Gongadze, but strangled him with a belt accidentally in the course of an interrogation. He is the highest-ranking official to be convicted in Gongadze’s death.