Who kills A in Pretty Little Liars?

Answer 1

'A', who is Mona, is killed by Spencer.

• Spencer finds out that Mona is 'A' and Mona tries to get rid of Spencer before she can tell anyone else. She tries to shove Spencer over a cliff and her plan backfires when Spencer shoves Mona over. So Spencer is the one who killed 'A' and then later a NEW 'A' arives.

This is a pretty good answer but I am not sure if you are talking about the book or tv show so on tv mona never dies she is sent. To the nut house and Hanna goes to visit her but she never talks and at the end of the episode she is sitting there while hanna walks out and the narrator In monas voice says something like "they think poor little Mona is helpless and locked up in a old nuthouse but that's what i want them to think." something like that happens

Answer 2

The first "A",Mona, was killed by Spencer
The first A was killed by spencer, after they got into a fight in floating man's quarry.