MOSCOW — A Ukrainian court sentenced a former security official to life in prison on Tuesday for the death of Georgy Gongadze, a journalist whose mysterious death in 2000 provoked an international outcry and helped set off protests against the president at the time, Leonid D. Kuchma.

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

Mr. Gongadze vanished in September 2000, and his body was found two months later, beheaded, in a forest 75 miles from Kiev, the capital. He had infuriated the president, Mr. Kuchma, with muckraking articles in Ukrainskaya Pravda, an Internet newspaper he had founded.

Suspicions of official involvement grew with the release of covert recordings made by one of Mr. Kuchma’s bodyguards, in which a man who sounded like the president spoke of Mr. Gongadze, telling a subordinate to “throw him out, give him to the Chechens.”