You know the legal concept of the smoking gun. But how about the smoking chainsaw? That came up this week in the great tree-cutting trial in Alexandria.

Most of the facts weren't in dispute. Developer Charles M. Fairchild wants to build a huge commercial complex on some land next to the George Washington Parkway. Last November hundreds of large trees on the property were suddenly cut down. Mr. Fairchild's son and two other men were seen sawing away. Nobody had a city permit to go lumbering. While lots of people thought the act was an outrage, Mr. Fairchild seemed to approve.

But did he violate the permit ordinance? A local judge, Robert T.S. Colby, threw out that charge this week. The city, he ruled, had failed to "put the smoking chainsaw in Mr. Fairchild's hands."

Well, maybe the wrong people were on trial. We hope the city will go after those who actually wielded the saws. Meanwhile, we wouldn't be at all surprised to hear Mr. Fairchild argue next that development is even more desirable since the woods have somehow been destroyed. He ought to realize that in the court of public opinion, where his project is on trial, people don't need ironclad chains of evidence to know who's doing wrong.