Were Gentiles lawless or merely not abiding by Jewish law? What difference does this make? A big one, I think. Translations that render lawless has connotations of being completely lawless. Those outside the law implies not holding to Jewish laws, but not necessarily without law. The rendering in the ESV and CSB imply that Gentiles were completely lawless, which can be misleading.
ESV: this Jesus, delivered up according to the definite plan and foreknowledge of God, you crucified and killed by the hands of lawless men. (also in CSB, NAB)
NIV: …and you, with the help of wicked men, put him to death by nailing him to the cross.
NRSV: …you crucified and killed by the hands of those outside the law. (also in NJB)
NLT: …“lawless Gentiles”; and NET: …“Gentiles”
Translations that render a-nomos (ἀνόμων) as “lawless” or “without law” may still be technically correct, but this might not have been the writer`s original intent.
Were Gentiles completely lawless? No, Roman society was ruled by law, particular by Law of the Twelve Tables;
or less lawful than Jewish society? Maybe;
or not living by Jewish laws? I think is this most probable.
I suspect the writer of Acts was simply trying to imply that Gentiles did not live by Jewish law but were not necessarily completely lawless. I find the NIV rendering is overly interpretive. The NLT`s is okay. The NET is inaccurate. Personally, I prefer the rendering of the last two translations NRSV and NJB on this one because it allows the reader to see Gentiles as only being “outside of Jewish law” but not necessarily without law.