Martha

Martha was a serial killer and Kenzie's accomplice. She killed Katie and Amy.

Killings
After Kenzie had killed Naoise, Katie discovered her body. Martha snuck up behind her and asphyxiated her with a baton. Still in her diguise, she then approached Amy. Amy thought that Martha was actually her boyfriend Johnny, but Kenzie had already killed him. Amy began to kiss Martha, who stabbed her with a razor glove.

She then met with Kenzie and discussed their crimes. Realising that they were the only ones left, the two turned on each other, and after a brief stuggle, Kenzie smothered Martha with a cusion. Kenzie then shot herself.