Gun makers could then see where problems might exist, he said.
"This is going to be a different day" for the gun makers, he said.
In recent years some gun makers have moved to make weapons less dangerous.
To gun makers, that is a sign of enormous market opportunities.
But he said it was now time to try to force gun makers to produce safer products.
The agreement does not end litigation by the cities against other gun makers.
But is there a third possible culprit - gun makers?
The first rifles used were imported from foreign gun makers.
But only in the last two years has the movement gained enough momentum to force gun makers to respond.
A number of civil cases are trying to hold gun makers responsible for deaths and accidents.