The explosion that downed a plane carrying Wagner Group leader Yevgeny Prigozhin and nine others in Russia was likely caused by a bomb, two U.S. officials told ABC News on Friday. Another U.S official said the United States believes that a bomb was very likely the cause of the explosion. The Kremlin vehemently denied having any involvement in the mysterious plane crash on Wednesday that presumably killed Prigozhin as well as Wagner Group co-founder Dmitry Utkin.