Robert Hare's research describes a recurring pattern in violent crime pairs: one dominant, persuasive partner does the planning and talking, while a more impressionable co-offender is talked into committing the actual violence. The dominant partner typically manipulates the other's insecurities or desire for approval rather than using force, which means the relationship looks, from the outside, more like an ordinary friendship or partnership than an exploitative one.
This dynamic matters beyond true-crime cases — it's a general template for how a manipulative person can get harmful actions carried out by someone else entirely, while remaining personally at a distance from the consequences. The "doer" often experiences the relationship as validating (finally being trusted, needed, or admired by someone) right up until the costs of the arrangement become impossible to ignore.