I think the fact that Danny was there and then devoted himself to the case was showing a great amount of support for Flack. I also think his punching the wall was in character. When Louie was brought to the hospital initially Danny had to be restrained and was screaming. When the guy who owned the car in which Aiden's body was found was brought in for questioning Danny again had to be restrained because he wanted to go after the guy. When Ruben was wheeled into the morgue Hawkes again had to restrain him and physically drag him out of the morgue so he wouldn't contaminate Ruben's body. I think punching the wall was a pretty subdued reaction from Danny. I agree.