How can Dietrich Bonhoeffer's inclusion of non-Christians be explained theologically?

I remember seeing a documentary about the life of Dietrich Bonhoeffer . One scene that was very interesting revolved around his leading a worship service in a transport between prisons, for all the prisoners, were he made some sort of special gesture to include non-Christian prisoners as well. Can anyone describe this event in greater detail. And could it be said to represent - some sort of use of worship as evangelism, (perhaps analogous to a small Billy Graham crusade) - a change in his beliefs to that of universal salvation, - or a belief in the appropriateness of interfaith worship under extreme circumstances?