A situation I made designed to make some sense but requires lateral thinking. Takes place in 2016 but in an alternate universe where we discovered a lot of technology earlier. Say WW2 or so.
An old man, 91 years old, with one leg sits in his wheelchair, in a white lab. A young blonde rimy man appears from the SAME room and strangles him to death with his own two hands, with clear anger in his eyes.
What could the reason be?
Edit: Edited this to make it less broad.