What made Merrett so remarkable as a criminal case was the combination of audacity and impunity — he shot his mother, beat his wife and mother-in-law to death decades later, and spent the intervening years as a fraudster and black marketeer, all while largely evading the consequences that would have stopped most criminals far earlier. His first trial ended in the distinctly Scottish verdict of "not proven," a legal ambiguity that effectively freed him despite strong suspicion, and the full scope of his crimes only became clear long after the damage was done. The gap between what he did and what he was made to answer for remains the defining feature of his story.

His appearances in Islamic State execution videos in 2014 and 2015 made him one of the most recognizable figures in the group's propaganda campaign, his masked presence and English accent carrying deliberate psychological weight aimed at Western audiences. The videos, which documented the killings of journalists and aid workers, were understood as sophisticated media productions as much as acts of violence. He was killed in a targeted drone strike in Raqqa in November 2015.

As second-in-command of the AUC, Mancuso operated at the apex of a paramilitary structure responsible for some of Colombia's most devastating civilian massacres during the country's long internal conflict. The organization he helped lead carried out violence under the banner of anti-guerrilla operations, but the toll fell heavily on rural communities with no combatant role. His eventual demobilization and cooperation with investigators offered partial accounting — though his extradition to the United States on drug trafficking charges underscored how deeply the AUC's operations were entangled with the cocaine trade that fueled the broader conflict.