What was the first (american) movie to introduce slashers/obsessive serial killers?

i've always thought it was Psycho, but then i watched Scream 4 and they mentioned that it was Peeping Tom. but then i checked online and found out that both of those movies were made in the same year (1960). so can someone who really knows film please answer this question for me? and again, this question is only referring to AMERICAN movies.What was the first (american) movie to introduce slashers/obsessive serial killers?Psycho is believed by many to be the first slasher film. However an earlier film, Thirteen Women (1932) has many slasher type qualities to consider it to be the first.What was the first (american) movie to introduce slashers/obsessive serial killers?The oldest one slasher film I know of is 2000 Maniacs and Bloodfeast, but there are probably older ones than that