OSCOW, March 5 - The chief of Ukraine's security service said Saturday that the country's former interior minister, Yuri F. Kravchenko, had shot himself twice in the head on Friday, refuting speculation that he had been killed by someone else. The official announcement and a note found in Mr. Kravchenko's pocket, the security chief added, left little doubt that Mr. Kravchenko had committed suicide. Advertisement Oleksandr V. Turchinov, chairman of the Security Service of Ukraine, said in televised remarks that the note left by Mr. Kravchenko could provide significant details for prosecutors investigating the killing of Georgy Gongadze, a prominent...