From The TimeSplitters Wiki

Scotland the Brave Secret Boss Glitch
Requirements	TimeSplitters: Future Perfect - Scotland the Brave unlocked
Finder	ILHI

When you go into the room with the lift where Crow escapes, if you move fast enough there is a way you can catch him and have a duel with him. He won't have gone down the lift and you can keep shooting him, he won't die, he's invincible. He does have a gun and he will shoot you. Run away and come back and it will all be fixed.