The marines shot at vehicles and other suspected threats for miles after the site of the March 4 incident in a village near Jalalabad in eastern Afghanistan, killing at least 10 people and wounding 33, Kearney told the newspaper.
"My investigating officer believes those folks were innocent ... We were unable to find evidence that those were fighters," the newspaper quoted Kearney as saying.
An official Afghan human rights investigation said the marines continued shooting for 10 miles, which the newspaper said Kearney did not dispute.
One marine suffered shrapnel wounds in the attack on the six-Humvee convoy, the newspaper said.
On Saturday, the Afghan rights commission issued a report saying the marines had acted illegally.
The unit involved was called home early soon after the incident.