Consider the starting time is the time when law and legal systems were being formed. The only difference I am trying to induce is the law itself which is stated as: If a person is found guilty of a murder and in state records it is his/her first murder, there will no legal implication. Except that the justice systems are the mostly the same as current. If you try to commit murder and you fail, you will be trialed normally for an attempted murder. State will prevent you from committing any murder even if it is your first, its only after you found guilty then it is checked if it was your first murder or not.
To narrow down the scope of "differently", just consider the following aspects
- Social relations of people with each other
- Most rewarding jobs and Any new jobs
- Impacts on gender equilibrium
- Which form of government would have prevailed OR any new form of government would have evolved