What detail should I be looking for in Leonard in Memento to determine the plot?
From what I understood after watching Memento, Leonard got the no of the car of Teddy and forgot where did he get it from and continued investigating with it. He noted the no just because Teddy told him his name also stands for Johnny G. But Teddy informed him that Leonard had already killed the killer, but he disbelieved him. Leonard had also jot down "Don't believe in his lies" under Teddy's picture because Teddy accepted not telling Leonard intentionally the truth that Teddy himself was a police officer working undercover. Later he also forgot why he wrote this for Teddy before killing him.
So what is true?
Leonard was really crazy who gave purpose to his own life for living by investigating already settled case of rape and murder of his wife?
Teddy was really his wife's killer?