I buy that interpretation because if Lex had prompted the kill, the halfway house guy would have been next, Lex wouldn't have let him be arrested and possibly talk, not if Lex already had proven he wasn't above murder.

ITA. Also, I think that the series itself isn't going to pass up the chance to show Lex's first *pre-meditated* murder on-screen (Nixon does not count, AFAIC, because that was in defense of Jonathan and the security guard in Onyx doesn't count because that wasn't *really* Lex). Lex stepping up to killing someone with malice aforethought is actually a pretty big deal in terms of his character development; they're not going to do that *off-screen*.