Английская википедия отмечает его успешную работу в Персии - в частности то, что он был одним из главных подстрекателей убийства Грибоедова.
A terrible event happened in the murder of the Russian Envoy, M. Grebaiodoff, and almost all his suite, by Persian rioters at Teheran. Though the Russian quarters were looted, and even the horses and horse clothing belonging to Russians which happened to be housed in the stable of the British Legation were carried off by the infuriated throng, they inflicted not the slightest injury upon a single article of British property. John McNeill was not at Teheran at the time, but in a letter to his wife (February, 1829) says: “The occurrence shakes all confidence and makes everyone uncomfortable, though, for my own part, I have not a doubt that I should have been as safe at Teheran as anywhere else.”
- Из «Мемуаров» д-ра Макниля.