Academy of Law
Judges Gibson and Dredd were friends during their training at the academy and after having a friendly fight, they promised that whenever they need to settle their differences, they will do the same thing.
Mutie the Pig
Gibson eventually became a bent Judge and began robberies under the alias, 'Mutie the Pig', and while Dredd was watching a security surveillance film during his most recent robber and noticed him supporting his gun-hand under his free arm instead of on top, which made him realise that he's a Judge in disguise and the technique is used by only three Judges Cicero, Gibson and Peace and due to Cicero confined to the hospital and Peace on a visit to Texas City, he found out it was Gibson and Gibson, watching, proceeded to assassinate Dredd to cover up his crime.
Their was a massive memorial for Dredd and Gibson then gave a speech about how Dredd was his friend and proceeded to light the Flame of Justice to honour Dredd. After the funeral, he disguised himself as Mutie and proceeded to rob a local bar, gunning down a man before he could draw his gun out. After the customers promised not to give him any more trouble, Dredd blasted the gun out of Gibson's hand and showed himself.
Dredd then arrests him and explains how since he suspected Griffin of being Mutie, he set himself as a target and Dredd felt the laser sight on him and managed to move a split-second before the bullet hit him. Dredd's memorial was then faked to trick Gibson into thinking he's dead so he'll commit another robbery and catch him during the act, proving that Gibson was Mutie. He then makes Dredd honour their promise during the Academy at Law and Dredd and Gibson prepare to fight to the death.
Fight to the Death
After Gibson chooses to fight at the Academy of Law in the simulation of a Mega-City One street, they proceeded to start fighting and Gibson fires a heat-seeker at Dredd. but he manages to avoid it by firing another heat-seeker at it, making them collide. Gibson then takes cover at the street corner and Dredd uses rapid fire, wounding Gibson and went to the street corner until Gibson reveals himself to be on top of the building and Dredd manages to gun him down. He asks the dying Gibson why he didn't just shoot him and states that he couldn't kill Dredd again and would rather die than be sent to twenty years hard labour on Titan. He then said "Goodbye... Old Buddy..." and Dredd wipes his name of the Judges list.