The one he bit is dead and the dog is going to be killed anyway.
What sense does the delay make at this point? Why not put him down right away?
To make sure no one was infected by saliva.
I used to have mastiffs. they were big, lovable drool machines, until they weren’t. Then they became vicious. It broke my heart, but I had to have them put to sleep. I couldn’t risk them killing a child or a trespasser or a meter reader, but they were fully capable of doing that.