Of course, dying in a slower, more painful manner than previously believed does nothing to diminish the witness of Dietrich Bonhoeffer, or to enhance it- a martyr's death cannot be quantified in that way. It is well attested by his fellow prisoners that right up until the time he was removed from the school in Schönberg, where they were being kept after their arduous and bizarre odyssey over the back roads of parts of rural Germany, even as he was being led away, that Pastor Bonhoeffer was composed and serene, even leading services on the Sunday, 8 April, the Sunday following Easter.
It bears noting that the footnote cited by Clements appeared in a work published twenty years ago and has not resulted in a serious revision of Bonhoeffer's last moments. Just taking the footnote at face value, it cites a Danish prisoner being held at the Flossenbürg camp, "L. F. Mogenson," as the source for the fact that "the executions of Admiral Canaris and his group were drawn out from 6 a.m. until almost noon." The assertion that the doctor, whose job sounded utterly evil, even more evil than that of the executioners, "could not have seen Bonhoeffer kneeling in his cell, neither could Bonhoeffer have said a prayer before his execution and then climbed the steps to the gallows. There were no steps" is not, at least not in the footnote (I have no idea what the main text relays), well-attested.
It does seem that the dubious nature of the testimony surrounding Bonhoeffer's last moments was taken into account by Schlingensiepen, who cites none of these when writing about Bonhoeffer's execution:
During the morning hours of 9 April, Wilhelm Canaris, Hans Oster, his colleagues, Theodor Strünck and Ludwig Gehre, Karl Sack, and Dietrich Bonhoeffer were hanged and cremated. Friedrich von Rabenau was to follow them a few days later. Their ashes, together with those of many thousands of other victims of Hitler's regime, form the now grass grown pyramid in the middle of the former concentration camp at FlossenbürgHere is something that is authentically from Bonhoeffer, a short commentary on Romans 13:1-7, which applies to governments: "No authority can legitimately interpret Paul's words as a divine justification of its existence... Those in authority... could never interpret it as a divine authorization of their conduct in office."