Romans 3:19-20 19 Now we know that whatever the Law says, it speaks to those who are under the Law, that every mouth may be closed, and all the world may become accountable to God; 20 because by the works of the Law no flesh will be justified in His sight; for through the Law comes the knowledge of sin.
Who is under the Law within the context of Romans 3? Jews? Gentiles? Both? Back in Romans 2 we read this:
Romans 2:14-16 14 For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, 15 in that they show the work of the Law written in their hearts, their conscience bearing witness, and their thoughts alternately accusing or else defending them, 16 on the day when, according to my gospel, God will judge the secrets of men through Christ Jesus.
The Torah was given to Israel through Moses. It seems that Paul is indicating a larger scope of the Law (knowledge of right and wrong?) that transcends the written commandments. This would be consistent with Paul's statement, "for all have sinned and fall short of the glory of God."