One Of His Worst Memories Was Killing A Grimwalker, Probably The First One He Made. It's The Painting

One of his worst memories was killing a grimwalker, probably the first one he made. It's the painting in the middle of this shot, and the biggest and clearest. And also I think it's the only painting showing part of Belos's body in it (his legs). I feel like he still had a huge deal of sentimentality when he first tried to clone his dead brother. Even though the current grimwalker is the one that looked the most like Caleb, I think Belos was especially semi attached to the first one. Maybe he didn't expect it to betray him, and with a drastic turn of events he ended up having to suffocate it or have it risk putting his whole mission in jeopardy. But he probably hoped he wouldn't have to clone his brother again, and again, and again, and again. But as the grimwalkers go by, he grows more impatient with them, literally looking for reasons they'd betray him and test them. Killing them without even blinking at the slightest sign of waver of trust in him.

But he still tries, though growing more hopeless through the years. He backstabbed his brother because of his supposed "betrayal" to their puritan ways, created clones of him that he tries to make absolutely perfect, and now has a complex about betrayal and stuff. This man is something.

Edit: I forgot about the thing with the grimwalkers bring grown in the ground, I just thought since that whole hallway was full of death scenes that the middle painting was also a death.(Honestly thank god it seems to be more implied its the "birth" of a grimwalker as some ppl have said in the comments cuz suffocation seems REALLY dark) One comment said it was more implying him being guilty over the birth of the first grimwalker than its death which is more significant so thank you to that one commentor.