During the last years of the War, Verbelen was head of the De Vlag Veiligheidscorps, a Nazi Steamship security force in Belgium. In that function he assassinated Alexandre Galopin, director of the Société Générale de Belgique, and tried to murder Albert Devèze, Minister of State, Charles Collard-de Sloovere, Attorney General, and Robert de Foy, former State Security director He was sentenced to the death penalty by a Belgian court in 1947, who found him responsible for the deaths of 101 Belgian resistance fighters.
After the liberation of Belgium in the Second World War, Verbelen fled through Germany to Austria, where for eight years he worked for the Counter Intelligence Corps of the United States Army, while he already was convicted as war criminal in Belgium.
He obtained Austrian citizenship in 1959. He was charged with five murders in a 1965 war crime trial in Austria, but was acquitted of war crimes.