He was later Private Secretary to a succession of British Prime Ministers: George Canning, Lord Goderich, the 1st Duke of Wellington, and Robert Peel.
It is generally thought, although the evidence is not conclusive, that McNaughton was under the impression that he had shot Prime Minister Robert Peel.
The McNaughton Rules developed by the House of Lords after his trial were to establish the basis for the insanity defence in all common law countries.
[1] In 1843, a surgeon who was opposed to blood-letting published an anonymous pamphlet claiming that Drummond was killed not by McNaughton's shot, but by the medical treatment he received afterwards.
[4] In the TV series, Drummond is killed instantly when he throws himself in front of an assassin's bullet to protect Peel immediately after the vote to repeal the Corn Laws.