He could address the first part of that - the bit about Marley not wanting that information getting out and telling them only what they need to know. Of course, he wants to say; he may have been a child when he started, but he didn't believe Marley was the entire world. Marley was the only option he had to making sure his father did not waste away and die before his eyes, though.

Bertholdt's eyes weren't truly opened until Paradis. To live in the ruin of what you created, to see a snapshot of life one hundred years ago. To see the animals trapped in the dark, as Eren so aptly put it. He could not other them for long, in the muck and misery. In the shadow of a man who hung himself, whose story they stole for their own needs.

To find a monster, they became monsters.

"We didn't --" He starts at first, then stops, closing his eyes for the briefest moment before he continues. "No one had made it inside. We didn't know what it was like... but we knew what it was like after we broke down your wall."

For now, he assumes 'setting them free' means what he did in Shiganshina; Bertholdt's death to save Armin, the fact that there was no opposition to them leaving the walls anymore. Eren achieved his goal of cresting the top of those ruined walls and breaking free.

(The truth is so much more horrific. The truth is no worse than anything else Bertholdt has ever done. What is a million people trampled to death when Bertholdt has wiped an entire city off the map?)

He does not apologize, though his tone is undeniably somber. Apologies would change and mean nothing no matter how sincere.