WMG / Friday the 13th (1980)

Jason killed Brenda

She was lured out with a child-voice calling for help. Also, when Pamela looked at her body, when she asked 'what monster did this,' she wasn't lying to catch Alice off guard. She was genuinely curious because she didn't kill her. Either Pamela's a good vocal imitator, or Jason has been doing some kills without his mother knowing.