Trying to identify title of horror movie I saw several times in my youth (early 1970s) on Chiller Theater (WPIX, NYC) It's a B&W from the late 1940s from my memory of the cars in it. Story line has a couple of doctors or scientists working in a lab on some kind of serum or drug. One of them, who I think lived in a room in the back of the lab, decides to drink/inject serum and transforms into a crazed murderer who stalks people at night. Under the influence of the serum his appearance pretty much remains normal except that his hair is disheveled, his eyes take on a crazed appearance and his lower lip droops, as if drooling . The crazed murder usually hides in bushes or behind trees, cars or in shadows between houses as he stalks his victims. There is one very tense , dramatic scene where a woman (I believe she is acquainted to the man in his normal state) is walking home alone one night and hears a noise that scares her. She increases her walking pace as she believes she's being followed and eventually starts to run. When she gets to her house she fumbles furiously with the key and makes it into the house and locks the door just in time as the man pounds on the outside of the door. He is eventually killed by the police. As it had a similar story line, I bought "The Creeper" (1948), but that was not the film. Thanks for any help.