Alhablaze

Hi every horror fan out there, Can any one help me im trying to find this movie, its a slasher movie from the late 70s its about a young blond hair guy that gets teased by these girls he takes revenge on them. I can only remember 3 scenes in the movie one seen there is a couple in a van I think it was blue the killer takes them out with a hammer. the other scene is in a work gym he putts a cable around the neck of one of the victims the other end has a dumbbell tried to it he throws it out the window. I think the movie has a black and white flashback when takes these girls out with a gun I think it fire small darts out of it. this is a crazy movie I watched it when I was 11 year old. the video cover was blue, maybe the movie was banned. if any one can help me thanks