I think the case your friend is referring to is that of "Fr. H." who sexually abused children in the archdiocese of Munich during the time when Ratzinger was archbishop of Munich. However, that was cleared up by the Vicar General, a Msgr. Gruber, who clearly stated that it was he who oversaw the reassigning of that priest and that he, not Ratzinger, is to blame for not taking "Fr. H." out of ministry when he should have.
Here is a link from an article by Whispers in the Loggia blog:http://whispersintheloggia.blogspot.com/2010/03/munich-admits-error.html
In other interviews, Msgr. Gruber explained that Munich was a massive archdiocese in the 1970's with over 1,000 priests and that Ratzinger was not involved in most personnel decisions as far as tracking these priests in hundreds of parishes and schools. Specifically, at no time did Ratzinger know a priest was a sexual abuser and move him into parish ministry.
Your friend's example of being a department head does not compare truthfully. Ratzinger's position was more like a CEO of a company with hundreds of branch offices scattered over a hundred mile radius. And a CEO cannot possibly know of every act of misconduct in a company with over 1,000 employees, not counting the sisters and lay employees who worked in churches, schools, hospitals, charities, and various ministries of the Church in Munich.
I hope this is helpful to bring some clarity.