Having brought the question up on Sunday in our meditation group, I received a link from one of our members to this site, where precisely this issue is discussed by one much more learned in the Buddha's teachings than am I. It's not only a discussion of this single issue, in fact: the essay is an extraordinarily fine encapsulation of Buddhist thought and practice, well worth reading for that wisdom alone. Here's a sample:
The path the Buddha taught is a deepening realization, without reduction to doctrine. Experiential apprehension of nonviolence replaces mere moral adherence to it. In the depth of realization of personal impermanence, certain truths become self-evident. All things are impermanent; all beings are transient; all beings suffer the common experiences of loss, decay, death. While each person, plant, or animal, has its own causes, its own seeds, that brought it into being, all share the bond of birth and death. Ultimately, nonviolence is a recognition of the simple facts that the quality of our life is the same as the quality of our moment-to-moment thoughts and feelings, and that enmity, hatred, and violence never improve our state of mind. Just as a man would not seethe with violence against his own body, he wouldn’t harm himself by seething with violence...period. Liberation means nonviolence.
The Buddha’s path begins with behavioral acquiescence to vows not to kill, but it culminates in an identification with nonviolence as the essence of what liberates the mind and heart from hate, fear, and self promoting delusion. "All fear death. Comparing others with oneself, one should neither kill nor cause to kill." [Dhammapada 129] Nonviolence is the essence of what the Buddha taught. Nonviolence is liberating because in each and every moment that it suffuses one’s mind, in that moment the mind feels compassion, identification, and empathy with other beings.
More specifically, on the subject of taking life, the author recounts this story:
In a poignant conversation that occurred when both the Buddha and King Pasenadi were eighty years old, the king praises the Buddha, his teaching , and the conduct of his followers, while describing himself as “... an anointed warrior-king, able to have executed those who should be executed...” After the king departs, the Buddha comments to the meditators around him that the King’s insights were “monuments to the Dhamma’ that should be learned and remembered as “fundamentals of the holy life.” [Majjhima 89] This passage clarifies that the Buddha neither condemned nor even rebuked the king for his fulfillment of the kingship, with its dire responsibilities.
I'm grateful to my friend for pointing me to this passage, because I was feeling very unsettled about my own conclusion, that I would have counseled von Boeselager to go ahead and shoot. It seems that the Buddha's wisdom and compassion embraces even those whom duty may compel to kill.