Open House (1987)

Dr. David Kelly is a psychologist who has a radio show where he gives advice.  He's dating real estate agent Lisa Grant, who the number one agent in the city.  There's also a killer targeting female real estate agents and an unscrupulous agent trashing other agents listings.

After each murder, the killer calls Dr. Kelly's radio show.  Kelly loses all perspective while trying to help the police track down this maniac and overlooks the possibility that his real estate agent girlfriend could be on the list of upcoming victims.

When the killer is revealed, you'll be amazed at the stupidity.