<p>A century of Illinois court decisions that a single-punch death isn’t grounds for a first-degree murder conviction prompted a Cook County judge Thursday to find the attacker of a Northern Trust bank executive guilty of a lesser charge of involuntary manslaughter.</p><p>Henry Graham sat impassively in a tan jail uniform with his hands folded as Judge Charles Burns delivered his verdict in the high-profile 2023 attack on Russell Long on the Magnificent Mile.</p><p>Graham came up behind Long and struck him in the back of the head. Long fell forward onto a North Michigan Avenue sidewalk and suffered a fatal brain injury. He died almost two weeks later.</p><p>“He was ambushed,” the judge said.