You realized that he targeted patients not only terminal and but also in tremendous pain. You made Samantha an attractive target. First you found the biopsy of a patient dying of cardiac cancer, you put Samantha's name on the results. You noted that her tumor was found during surgery and then you placed them into her chart. Secondly, you made sure she was in pain so the Angel would feel compelled to end her suffering, that was simply, pull back on her pain meds. This had the added benefit to make her delirious and not be able to communicate to the killer who liked to chat up his victims and he took the bait. Samantha had succumb to her cardiac event. All you had to do was remove her cancer results from her chart and your mistake was erased.

Sherlock