<P> At the camp, counselors Ned, Jack, Bill, Marcie, Brenda, and Alice, along with the owner Steve Christy, refurbish the cabins and facilities . As a thunderstorm approaches, Steve leaves the campground to stock supplies . Meanwhile, the killer arrives at the camp and stalks the counselors . Ned sees someone walk into one of the cabins and follows . As Jack and Marcie have sex in one of the cabin's bunk beds, they are unaware of Ned's body directly above them, with his throat slit . Soon after, Jack is killed when his throat is pierced with an arrow from beneath the bed, and the killer murders Marcie with an axe slammed into her face . Brenda hears a child's voice calling for help and ventures outside her cabin to the archery range, only for the range lights to turn on as she is attacked off - screen . Steve later returns to the camp and is confronted by the unseen killer, who stabs him . </P> <P> Alice and Bill are worried by their friends' disappearances, and they leave the main cabin to investigate . They discover a bloody axe in Brenda's bed, the phones disconnected, and the cars inoperable . When the power goes out, Bill goes to check on the generator and is murdered by the killer . Alice then heads out to look for him . Upon finding Bill's body impaled with arrows to the generator room's door, she flees back to the main cabin to hide only to be traumatized further when Brenda's body is thrown through the window . </P> <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 begins to reminisce that her son Jason was the young boy who drowned in 1957 . She blames his death on the counselors who were supposed to be watching him, but they instead were having sex and 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 a tree . 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 with a machete . During the final struggle, Alice ultimately decapitates Mrs. Voorhees with her machete . Afterwards, a traumatized Alice boards and falls asleep inside a canoe, which floats out on Crystal Lake . </P> <P> Just as Alice awakens and sees the police arriving, Jason's decomposing body suddenly emerges from the lake and drags her underwater . She then awakens in a hospital, where a police officer and medical staff tend to her . When Alice asks about Jason, the officer says that there was no sign of any boy . Alice says, "Then he's still there," as the lake is shown with a single ripple on the open water . </P>

Who did the killing in the first friday the 13th movie