What should be done if a man has sex with a betrothed virgin in the city?

Stone them both to death.

The woman because she didn't cry out (being in the city).

And the man because he humbled his neighbor's wife.

If a damsel that is a virgin be betrothed unto an husband, and a man find her in the city, and lie with her;

Then ye shall bring them both out unto the gate of that city, and ye shall stone them with stones that they die; the damsel, because she cried not, being in the city; and the man, because he hath humbled his neighbour's wife: so thou shalt put away evil from among you. Deuteronomy 22:23-24