Was Dietrich Bonhoeffer a “martyr” in the traditional way that Christians understand martyrdom?

Craig J. Slane, in his book, Bonhoeffer as Martyr, writes that we should not be that quick to see Bonhoeffer as a martyr.

Upon his return from New York in 1939, Bonhoeffer involved himself in various acts of subterfuge against the German government, and as an active member of the Abwehr he participated in tyrannicide by plotting to assassinate Adolf Hitler. It was for his participation in this treasonous conspiracy that he was ordered hanged by the Gestapo. The Gestapo saw only his “high treason.” On the surface at least, Bonhoeffer’s Christian conviction in the matter seem to have been an irrelevant fact in the immediate circumstances of his death. Hence this final and highly politicized period of his life (1939-1945) renders ambiguous the relationship between his Christian confession and his death and thus calls into question the authenticity of his martyrdom when weighed against the traditional Christian understanding (29-30).