その事件は残忍冷酷な犯行として報道された。
The incident was reported as a brutal and merciless crime.
残酷 is a more common word for 'cruel' or 'brutal', while 残忍冷酷 emphasizes both cruelty and cold-heartedness together.
冷酷 means 'cold-blooded' or 'heartless', focusing on lack of emotion; 残忍冷酷 combines this with 残忍 (brutality).
Compound of 残忍 (ざんにん, 'brutal') and 冷酷 (れいこく, 'cold-blooded'). The exact historical derivation is uncertain, but the spelling is conventionally associated with the combined meaning.