Given Mr. Beck's primary motivation of getting the SOB that shot him, I'm sure he would have been disappointed.
I guess I'd tend to think that was a pretty darned good motivation under the circumstances; others may differ.
If someone is snooping around your house at night, and flees as soon as they're aware they've been noticed, there's no way of knowing what their exact intentions were regarding you or anyone else. Part of the reason for the general prohibition against shooting fleeing criminals is that one cannot always be sure what the person was up to, or how much danger they posed to others.
In the extant situation, the man had just been shot in cold blood. Although I doubt he thought things through in detail, I'd say his gut instinct was right on: to do whatever he could to stop his shooter from getting away. Although his motives were far more personal than society-oriented (he did not want to die unavenged), I would suggest that as a citizen he had a right and duty to prevent the escape of someone who had willfully shown himself to be extremely dangerous.
Further, even if you judge that Mr. Beck's actions were unacceptable, I think there should be certain lattitude given to people who are forced into situations of extreme duress. Although I think the term "temporary insanity" is overused, I think it should be reasonably applicable to situations where a person was subjected to trauma outside their control and their judgement was impaired as a result.
To put it another way, even if it is found that Mr. Beck posed a danger to society shortly after he was shot in the head, that would not imply that under 'normal' circumstances he would be any danger to society, nor that the level of danger he posed was excessive compared with that posed by anyone else in the same circumstances.
Nearly anyone can 'snap' under the right circumstances. People have a duty to do what they can to avoid situations where they might 'snap'. People who voluntarily get into a situation that causes them to snap should be held accountable for their actions. But people who are involuntarily forced into a situation that would cause just about any normal person to 'snap' should not be held so accountable.
He did not however have the right to take a shot at that woman. It was entirely unjustified, regardless of what happened to him, or any claim of duty to prevent escape.
The right to life is absolute. Unless you can show the woman was not in Beck's sight picture, there is no justification for the particular string of shots that perforated both individuals twice.
" I think there should be certain lattitude given to people who are forced into situations of extreme duress"
Regarding this case, at trial and sentencing. He should have been indicted for reckless endangerment, or the equivalent. See once innocents enter the sight picture, you keep your finger off the trigger. The shot belongs to a marksman, not the pray and spray expert.