For me, the important part is the "after rationally considering" part.
Tragic as it would be, if it had been a violent argument where he started waving a gun around, I doubt he would be rationally considering very much.
I guess if they were arguing THEN he got the gun then he'd made a choice but if he already had the gun in his hand then it could be a fit of rage.
Hold on I am considering that people argue with guns in their hand?!!! What has this case turned us all into - we just dont have this kind of thing here in the UK but it seems normal after this week on here to even consider it.