Conversation so far:
What was the detection of Harold Shipman?
Harold Shipman was detected when concerns were raised about the high death rate among Shipman's patients.
Are there any other interesting aspects about this article, besides the detection of Harold Shipman?
In particular, she was concerned about the large number of cremation forms for elderly women that he had needed countersigned
What was Harold Shipman being investigated for?
Harold Shipman was being investigated for murder

Question: How did he kill them?
Self-contained rewrite: How did Harold Shipman kill them?