<P> Alice sees a vehicle pull up and rushes outside , thinking it is Steve . Instead , she is greeted by a middle - aged woman named Mrs. Voorhees , who claims to be an old friend of Steve 's . As Alice brings her inside , Mrs. Voorhees reveals that her son Jason was the boy who drowned in 1957 . She blames his death on the counselors who were supposed to be watching him but instead were having sex , not paying attention to Jason 's drowning . Revealing herself as the killer , Mrs. Voorhees turns violent and rushes toward Alice with a bowie knife , attempting to kill her . In the ensuing chase , Alice finds Annie 's body inside Mrs. Voorhees ' car and Steve 's body hanging from the roof . Following a confrontation in which Mrs. Voorhees is knocked out , Alice escapes to the shore . Just as she begins to relax , Mrs. Voorhees finds her and attempts to kill her again . During the final struggle , Alice decapitates her with a machete . Afterwards , a traumatized Alice boards and falls asleep inside a canoe , which floats out on Crystal Lake . </P>
who does the killing in the first friday the 13th
Mrs. Voorhees