Yes. It is his story. The only one we have right now. Unlike all of your baseless conjecture.
Correct. Which is why I assuming that it is accurate, despite several implausible features.
Unlike all of your baseless conjecture.
I haven't conjectured.
I have pointed out certain flawed assumptions - for example, the assumption that Smith has the expert knowledge to assess that someone is beyond the reach of medical help.
As you commented earlier, Smith is "highly intelligent" and a "retired professional" - in point of fact, a retired professional in the field of law enforcement.
If a highly intelligent retired LEO had killed two intruders on perfectly justifiable grounds, then he would have naturally followed protocol - armed himself, then called 911 when he heard what he thought were burglars' footsteps, then taken any necessary actions in self-defense.
His actions were pretty close to the opposite of what a highly intelligent retired LEO would do if he were innocent of wrongdoing.
The story he told - after two days of living with corpses rather than reporting the break-in - is likely the least damning story a "highly intelligent" man in his situation could come up with, that would still fit the physical evidence.
As you say, his story is the only coherent account of the incident we have so far - but it is just barely coherent.
And an observer has to wonder why.