Rom 2:12-15
12 For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law;
13 (For not the hearers of the law are just before God, but the doers of the law shall be justified.
14 For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves:
15 Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another)
The Moral Law is written on the natural mans heart, thats why he knows stealing is wrong, killing is wrong
The Law in Vs 15 in the original has the definite article so Paul is speaking about the Moral Law given to Moses, the Ten Commandments.
All men whether jew or gentile naturally under the law of God, i m surprised you didnt know that. Rom 3:19
19 Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world[Jew/Gentile] may become guilty before God.