Asked if Zimmerman should face federal civil rights charges in the death of Martin, who was black, Warren said the Justice Department is considering the question, but the jury has spoken.
The Massachusetts Democrat said the goal should be to create a country "not just where some of us are safe, but where all of our children are safe."
Fellow Democratic Sen. Edward Markey questioned whether the laws might embolden someone who is armed to pursue an unarmed individual and then fire if that person turns to confront them.
He said it's time to start "paring back" the laws.
Massachusetts doesn't have a stand your ground law.