TCM says:
One night, when Cheryl Draper wakens and gets out of bed to close her bedroom window, she sees a man, Albert Richter, strangling a young woman to death in an apartment across the street. Cheryl phones the police, but before Lt. Lawrence Mathews and Sgt. Eddie Vincent arrive to interview Richter, he hides the body in an unoccupied apartment next door and pretends to have been asleep. After they find nothing to incriminate Richter, Larry suggests to Cheryl that she may have dreamed it all, but she is adamant that she saw the murder.
http://youtu.be/BnkhXuBLRpk