In the Timeless Universe
In the original timeline, Seward is stabbed by Powell, but is merely injured and survives. Powell then flees.
In the altered timeline, the conspirators (including Powell) are armed with modern handguns by Garcia Flynn. Powell attempts to assassinate Seward with the new gun, but is blocked by Wyatt Logan. A fist fight between Wyatt and Powell ensued. During the fight, Fanny Seward, William Seward's daughter, witnesses the battle and calls for her father to come and see what is happening. Wyatt kills Powell with two shots to the abdomen. When Seward asks Wyatt what's going on, Wyatt flees.
William H. Seward at Wikipedia