In Pretty Little Liars how do they find out that A is Ali?

Answer 1

Ali, posing as her sister courtney, comes back to rosewood, tells her old best friends she is ali but for them not to tell anyone. Ali takes the girls to a vacation spot they used to go to when they were younger and hypnotizes them like she tried to when they were in grade seven, while they are all asleep she leaves a letter explaining she was A and then burns down the house trying to kill them all, Melisa who was in the closet, and destroy Ians corpes that was also in the closet ontop on melisa.