Wow, is that ever a question he never intends to answer honestly.

He could do it, if he could give any of the reasons Fontaine fed him. He could do it, if he could even say that yeah, I heard enough, I wanted to kill him.

He could answer, if he knew for sure that, when everything came together and he realised what was happening, he still would've done what he did without the influence of that phrase.

"Doesn't matter," Jack tells the floor roughly. "He's dead."