He would be condemned and no doubt put to death for such a crime. Even though his motive for committing the murder was in the public interest, murder is still murder in a civil society, and cannot be condoned under any circumstances.
Rousseau believed that freedom, rationality, and morality are only possible in civil society, and civil society is only possible if the people agree to a civil contract (Sparknotes). We are only human if we are active participants in society. If the only way to be fully human is under a social contract, the contract becomes more important than the individuals who agree to it, and those individuals only have value if they agree to the contract. The contract is not agreed to individually be each person, but is affirmed by the group collectively, making the group more important than the individual. The sovereign and the general will are more important than its subjects and their wills. General will may direct the state to achieve the goals of the common good, and sovereignty is indivisible and inalienable (Halsall).
Though Rousseau believed that rationality and morality were only possible in a civil society, he also believed in a man retaining his individual freedom and not losing his individual power, which gives a mixed message as to how he would regard John's killing of the old man. On the one hand, being part of a civil society, with morality and rationality, he would be condemned, while on the other, exerting his own p