Aaron Copley
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Aaron Copley was a physician and scientist working in Wales. He captured alien species, and tried to create vaccines for human illnesses. He knew they were going to die but he needed to find a way to cure human illness and he used a species called the Mayfly. He also had a Weevil in containment.
He shot and killed Owen Harper and was shot by Captain Jack moments later while threatening to shoot Martha Jones. (TW: Reset)