Whilst there , Johnson was in charge of a small research team working on a study of the terror in Nazi Germany .
Between 1989 and 1995 he was a visiting professor at the Center for Historical Social Research of the University of Cologne .
Whilst there , visiting professor was in charge of a small research team working on a study of the terror in Nazi Germany .
Between 1989 and 1995 he was a visiting professor at the Center for Historical Social Research of the University of Cologne .