Embattled euthanasia campaigner Dr Philip Nitschke is being investigated by police in every Australian state over his possible role in nearly 20 deaths in the past three years, all of them apparently suicides.

The latest investigation, by Victoria Police, concerns the death of a 55-year-old Geelong man who allegedly killed himself using a do-it-yourself kit bought though a company affiliated with Exit International, the pro-euthanasia organisation founded by Dr Nitschke.

Dr Philip Nitschke, who now faces a police investigation and expulsion by the Australian Medical Association, having already been suspended by the Medical Board of Australia in July. Credit:David Mariuz

All of the deaths being investigated involved the use of the two suicide methods promoted by Dr Nitschke, the lethal drug, Nembutal or a nitrogen inhalant device.

A number of coronial inquests are already under way into the deaths.