They knew folks were getting shot with a 5.56, they had bullets but no gun. So they went through the records to find who had guns and then took them for testing. Recall that they were busy looking for a white man because that's what their profile said it should be.
Did you really not see the Boston marathon bombing aftermath when they thought the guy was in this neighborhood, so they pulled everyone out, house by house and searched? He was in a boat in a backyard, someone called and told them I believe. In the meantime they did random searches of private residences with no real direction or evidence.second going from house to house in search of suspect is standard police procedure not sure what you mean pulling people out of their houses. They were searching for armed suspects they asked people to step out and help in the search yes with guns pointed out like you do when you are looking for dangerous people.