This paper aims to showcase how the European Court of Human Right interpreted the criteria for an effective investigation under Article 2 of the European Convention on Human Rights. Through detail analysis of four landmark cases which occurred during the Northern Ireland Conflict, it evaluates how the European Court has shaped the standards for conducting investigations of the legality of use of lethal force by the law enforcement forces. The focus is thereby placed on the importance of independent, transparent, and prompt investigation that ensures public scrutiny and the participation of victims’ families. By assessing the effectiveness of investigations involving the use of lethal force, the paper provides crucial insights into how the European Court has refined its guidelines, offering more precise standards for national courts across Member States. There is also a further exploration of the critical perspectives on the impact of these judgments there influence on the evolution of international legal standards in contexts affected by conflict.