That part of Dahlgren's speech provides no suggestion of assassination. Indeed, it suggests that the first option would be to capture them. Of course, if they were shot trying to esacape ...
As far destroying and burning the "hateful city" of Richmond, that seems to be a legitimate military goal. Not only was it the site of the insurrectionist government, but it contained numerous factories, warehouses, and armories that aided the war effort. In many ways, it is too bad the confederates burned it to the ground before the Union had the opportunity.
"Of course the military determines what is lawful, eh?"
Where the Laws of War, rather than the rule of law, prevails - YES.
Don't go by me.......ask one of your buddies if your posts make you look hateful and small. If they're sober when you ask them, they might tell you the truth.
Somebody open a window.
We will try and secure the bridge to the city, (one mile below Belle Isle,) and release the prisoners at the same time. If we do not succeed they must then dash down, and we will try and carry the bridge from each side. When necessary, the men must be filed through the woods and along the river bank. The bridges once secured, and the prisoners loose and over the river, the bridges will be secured and the city destroyed. The men must keep together and well in hand, and once in the city it must be destroyed and Jeff. Davis and Cabinet killed.