[The murders, he's guessing, or perhaps more accurately, the aftermath of that trial. Though maybe Alexei's just referring to their time in murdergame hell in general, which is very, very fair.]

I imagine that was difficult for the first little while! Somehow, neither of you seem the type to sit and talk about [vague handwave] all of that.

[That's a little lighter, but not properly a joke or teasing.]