Russia: Expressing condolences for the victims of the hostage incident.
Literal
Russia: hostage-incident [possessive-の] sacrifice became people [to-に] condolence [possessive-の] meaning [object-を] express.
A news headline using formal diplomatic language. 哀悼の意を表す ('to express condolences') is the fixed diplomatic formula — 哀悼 'mourning/grief,' 意 'sentiment,' 表す 'to express.' 犠牲となった ('who became victims') uses the formal ~となる. The colon after ロシア is headline formatting, with the country as the actor.