I'm gonna go out on a limb and say if the old man would hypothetically be unable to detain the 20-something man, he'd also be unlikely to choke him to death...
I also like the idea of a thief being caught...though, as FP pointed out, what if it was your sister's misguided 20 year old son who got himself killed for attempting to steal an outboard motor to support his drug habit? You'd be screaming for the old guy's head, and don't for one second lie to me and tell me you wouldn't.
If it went down like the old man said, and his life was in danger, then it should be an open and shut case of justifiable homicide. At this point, I find this scenario highly unlikely to be the truth.
If there was an attempted burglary that went awry, and the old man killed the kid without his life being in danger, then the old man is going down, and should...I don't care how old you are, you can't go around killing people over a few hundred or a few thousand bucks worth of outboard motor. This isn't the Wild West, or some fuckedup third world country. Probably not Murder One, but something that won't have him out any time soon.
That's probably the most likely scenario, from what I've heard so far.
The last scenario is cold blooded murder with a setup to make it look like a burglary. If this is what happened, then the old man should be explaining himself to his Maker as soon as practicable.
Unfortunately I find this scenario to be more likely than the original story the old man told.
Fish on...
Todd
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Team Flying Super Ditch Pickle