Following numerous 'failed' cases at the criminal courts of appeal over the last decade, the principle of reviewing ongoing murder inquiries was adopted by the police forces of the United Kingdom. This study sets that process into the historical context and through a review of the literature, develops a benchmarked review template or 'tool' to assist the review of a murder inquiry against national policy, good practice and academic research. The tool was evaluated by an experimental group of six investigators examining a murder using the tool and comparisons made with a matched control group conducting a review on the same murder without using the tool. The resultant quantitative and qualitative analysis showed that the experimental group produced significantly more review comments which were of a consistently higher quality than the control group. From this research several recommendations are made, including the adoption of the review tool nationally through the National Police Improvement Agency. This research aims to assist reviewing officers' to complete reviews in a more structured and consistent way, avoiding the pitfalls of flawed investigative mindset, identifying new lines of inquiry and capturing learning which can help future generations of senior investigators and lead to a perpetual cycle of professionalizing the investigative process. (Published Abstract) Figure, tables, references, and appendix