In North Korea from 1999 to 2001, Vollertsen practiced medicine with the Cap Anamur Committee, a non-governmental cooperation organization.
[3] As he traveled in his capacity as an emergency physician, visiting the countryside and tending to the illnesses and injuries which common North Koreans were suffering from, he struggled with a nearly non-existent healthcare system, abject poverty and growing proof of a network of political prisons in North Korea that enforced the flow of wealth from the citizenry to the Pyongyang-based military and the Workers' Party of Korea which was then headed by Kim Jong Il.
Using smuggled cameras, he obtained photos and films of flagrant, large-scale human rights violations in North Korea.
He began to collect evidence of human rights abuses, which he passed to a visiting United States Congress man, an act for which he was put under surveillance.
His wife, reacting to his decision to stay in South Korea as an anti-Kim activist, divorced him and she is raising their children with a partner.